Nexus: The Jupiter Incident

Realms of Chaos
Raptor
Another World
Serious Sam: The First Encounter
Elder Scrolls III: Morrowind (or at least, it doesn't appear for me when I search for it, and I have too many to look for it.)
the Alien Shooter games
the Alien Breed games
Gothic 2
Mount & Blade: With Fire and Sword
Shadow Warrior: Classic Complete
Shadow Warrior (Reboot)
Divinity 2
Divinity Original Sin 2

I'm guessing this is a quirk that has to get ironed out?

Added the games named by bela, SCPM, DampSquib and InkPanther! Thanks for your additions.

You could always search for the games you suspect are missing their backgrounds on the personalization page.

Check again to see if they do have backgrounds, and ask your friends who own these games if any.

One interesting thing I noticed is that the background for Shantae and the Pirate's Curse is actually artwork lifted from Shantae: Risky's Revenge. I don't know why or how that is.

Sometimes it takes a while to load or something. I've had to click the game I want as a background, click another random one, then click the one I want AGAIN for it to load. Just fyi.

SWAT 3 and XIII(removed from store) are missing from the backgrounds ;).Cheers

I checked on another device, so it's at least not an issue with my desktop setup. I currently have one of them set as my background, so you can go see for yourself.

I guess I'll send a bug report about this, even though I quite like the black background...

Grim Fandango (already listed) has no background. Excuse me but I'll rip a tiny little rage.

You're right.

I also see a black background on your end. Oh my.

Guess I'll be adding them with a disclaimer that there is a background with these games, but they're black. :/

Hostile Waters: Antaeus Rising
Waking Mars
Europa Universalis: Rome Gold (EU3 Complete has one though)
Icewind Dale Complete - not on sale
Toonstruck
Richard & Alice
Hearts of Iron II: Complete (Darkest Hour has one though)
Shelter
Race Driver: GRID - not on sale
Sam & Max Hit the Road
Deadly Premonition: Director's Cut
Beyond Good & Evil
Dark Fall 2: Lights Out
Desperados: Wanted Dead or Alive
STAR WARS™ Knights of the Old Republic™ II: The Sith Lords (first KotOR has one though)
Men of War: Red Tide
Soldiers: Heroes of World War II
Myst 5: End of Ages
The Shivah
Pathologic - not on sale
American Conquest
Cossacks Anthology
The Whispered World: Special Edition
Total Overdose: A Gunslinger's Tale in Mexico
Night of the Rabbit
Goodbye Deponia (although first two have backgounds)
Risen
Risen 2: Dark Waters
A New Beginning: Final Cut
Back to the Future: The Game
Arcanum: Of Steamworks and Magick Obscura
Machinarium
The Last Express
The Bard's Tale
Tropico 1 and 2

Sam & Max: The Devil’s Playhouse
Sam & Max Beyond Time and Space (first season has one though)

Witcher 3 has background image.
probably it's worth to mention in respective entries that Gothic 1 and Dreamfall: The Longest Journey have profile background images.

since it's just backgrounds from store pages, i really don't get why some of them are missing. maybe they're working on alternative versions? it'd be cool to use Red Tide cover art among others.

I have a background for D:OS 2 (attached).

Quite right, I didn't see it because it isn't a title I own yet. :S

An Elder Scrolls Legend: Battlespire
Anno 1404: Gold Edition
Assassin's Creed®: Director's Cut
Atlantis 2: Beyond Atlantis
Atlantis 3: The New World
Atlantis: The Lost Tales
Baldur's gate: the original saga (removed)
Banner Saga 2
Battle Chess Special Edition
Battle Worlds: Kronos
Black Mirror 2
Blackwell Bundle
Broken Sword 2: Remastered
Broken Sword 3: The Sleeping Dragon
Broken Sword 5 - the Serpent's Curse
Caesar
Caesar 3
Carmageddon 2: Carpocalypse Now
Celtic Kings: Rage of War
Cognition: Game of the Year Edition
Colonization, Sid Meier's
Commandos Ammo Pack
Commandos 2+3
Conquests of Camelot: The Search for the Grail
Conquests of the Longbow: The Legend of Robin Hood
Corsairs Gold
Dark Reign + Expansion
Desperados: Wanted Dead or Alive
Disciples 2 Gold
Disciples: Sacred Lands Gold
Disney Aladdin
Disney The Jungle Book
Disney The Lion King
Eador. Imperium
Eador. Masters of the Broken World
Elder Scrolls Adventures: Redguard, The
Empire Earth 2 Gold Edition
Empire Earth Gold Edition
Eschalon: Book II
Fallen Enchantress: Ultimate Edition
Fallen Enchantress: Legendary Heroes
Fallout 2 classic (there is a background for Fallout 2)
Fallout classic
Fallout tactics classic
Freddy Pharkas: Frontier Pharmacist
Gabriel Knight 2: The Beast Within
Gabriel Knight: Sins of the Fathers
Gobliiins pack
Heroes Chronicles: All chapters
Heroes of Might and Magic® 5: Bundle
Heroes of Might and Magic® 2: Gold
Heroes of Might and Magic® 4: Complete
Imperialism 2: The Age of Exploration
Indiana Jones® and the Fate of Atlantis™
King Arthur Collection
King's Quest 1+2+3
King's Quest 4+5+6
King's Quest 7+8
Knights and Merchants: The Peasants Rebellion
Konung 1 + 2

Haven't seen a background for Neverwinter Nights or Rune classic.

Labyrinth of Time, The
Lands of Lore 1+2
Leisure Suit Larry
Leisure Suit Larry: Love for Sail!
Leisure Suit Larry: Reloaded
Lords of Magic: Special Edition
Lords of the Realm: Royal Edition
Lost Eden
Majesty 2 Collection
Master of Orion
Master of Orion 1+2
Might and Magic 6-pack Limited Edition
Might and Magic 8: Day of the Destroyer
Mortal Kombat 1+2+3
Myst Masterpiece Edition
Patrician 1+2
Pirates! Gold Plus
Police Quest Collection
Prehistorik 1+2
Quest for Glory 1-5
Rain World (bugged)
Real Myst Masterpiece Edition
Incredible Machine Mega Pack, The
Return to Mysterious Island
Riven: The Sequel to Myst
Robin Hood: The Legend of Sherwood
Settlers 2: 10th Anniversary, The
Settlers 3: Ultimate Collection
Seven Kingdoms: Ancient Adversaries
Sid Meier's Alpha Centauri Planetary Pack
Space Quest 1+2+3
Space Quest 4+5+6
SpellForce 2: Demons Of The Past
Stronghold Crusader HD
Tex Murphy: Mean Streets + Martian Memorandum
The 11th Hour
The 7th Guest
The Adventures of Willy Beamish
The Black Mirror
The Book of Unwritten Tales
The Book Of Unwritten Tales: The Critter Chronicles
The Colonel's Bequest
The Dagger of Amon Ra
The Dig
The Guild 2
The Guild 2: Pirates of the European Seas
The Guild Gold Edition
The Legend of Kyrandia(Book One)
The Legend of Kyrandia: Hand of Fate (Book Two)
The Legend of Kyrandia: Malcolm's Revenge (Book Three)
The raven: legacy of a master thief (the remastered version has a background)
Thimbleweed Park
Torin's Passage
Total Annihilation: Commander Pack
Total Annihilation: Kingdoms + Iron Plague
Tzar: The Burden of the Crown
Wasteland 1: The Original Classic
Wasteland 2 Director's Cut Digital Classic Edition
Wizardry 6+7
Worms 2
Worms W.M.D
There are backgrounds for both Neverwinter Nights (attached).