It's because the individual games are actually remakes of the games from the complete saga, with a lot of changes made.
Interestingly enough, the original Avernum games are, themselves, remakes of the old Exile games.
If you don't know which one to get, there are demos available. https://www.spiderwebsoftware.com/avernum/avernumold/index.html http://www.avernum.com/avernum
(Saves from the demo should work on the full version.)
I directly marked my question, and as it said: "Mark as "question / problem" (special category of "help me" topics that encourages others to answer and earn reputation points for solving your question / problem; offtopic chatter is forbidden."
I done this to encourage people to strictly post about the exact question that I asked, because I really sick of reading through hundreds and hundreds of useless posts, wastes hours looking for answers, just to find a tiny bit of information that maybe have something to do with what I looking for.
I done this to avoid posts like yours. Sorry, but I didin't asked anything like that, what you posted about. I nowhere asked about the origination of the game: I didn't asked about which game is a remake of which other game, or about demos of the games.
I asked about (because I realised the huge file size and price differrence) what other things, like the goodies, are come with the individual game which isn't part of the saga.
Or somthing like that, becase it just bugs me so much, how is that possible that 6 games bundled together is smaller than even 1 game. I need indepth, technical explanation about what comes with the individual games, and what comes wih the saga, that explains the huge file size difference. Especially about the goodies, that what I aseked.
Regardless that I can't accept your post as an aswer, thanks fot the info that the saga contains outdated version of the games and that the individual games are improved, later versions (hence the much higher price) of the games. Or whatever you mean by that meaningless "with a lot of changes"... At least it is a bit more information about the games.
Still, I like to know about what goodies the games and the saga contains exactly, so that I can compare them to eachother. If the file size and price difference not just because of the goodies, I like to get more technical explanation what are the difference that makes that huge size difference.