Note I'm NOT whining about GOG
I'm just curious why there are so many indie adventure and plat former type games in general?....even on Kickstarters to my dismay ( I had hoped for a lot more variety of games in different genres )

Easiest games to make.
For adventure games, find a story, insert challenges at some points, and you have a game.
For platformers, you have your basic movement and maybe attack, then a background story as filler, then it's about level design and gimmicks.
In both cases, you can make a linear game without that many paths to take, and still have a decent game. Most of the other genres do require quite a bit more commitment.

Maybe many people (including myself) want and buy them?

Yep, I am also glad that adventure games had a resurgence and now we are getting more of them like in the good old days. :)

I was never way into platformers but when I was a kid growing up in the 80s at the arcade those were hands down the machines that got the most attention. Donkey Kong of course was "King" but games like Joust were also big. I may be talking out of my ass here but back then of course it was 25 cents per play which could add up especially if there was a nasty learning curve or a lot of rules.....the classic platformer never had any of that...run/jump/shoot/repeat. Last time I was in a full on real life arcade the first Mortal Kombat cabinet had just come out and here were these kids spending $100 just to master a slide kick. XD If you had the dough that's all well and good but most couldn't push that and the platformers still got the bulk of the business: no complicated moves, run/jump/shoot/repeat.

Can you name a few of the many retro-styled puzzle platformers that are graphically reminiscent of the 8-bit and 16-bit era, apart from Escape Goat? In any case, I think that's just it: There are so many puzzle platformers today because there weren't that many back then and it's the new cool. Not just because developers jump on the bandwagon of successful titles, but also because they find it interesting to toy around with the new options and opportunities. And the "retro" graphics are a consequence of small budgets and many developers being the same kind of nostalgic geeks that you find here, people who just like pixel art.

Oooh yeah. :)
Not a fan of platform, but I grew up on adventure games, and they nearly disapeared from my radar for a long time. I'm quite happy they made a comeback.

Yes and no.

In the case of (puzzle) platformers, as people have said, it's simply because they're easier to make. I'm yet to see (m)any puzzle platformers that have been financially viable.

With adventure games, there has certainly been a drought for several years, but again, AGS has enabled them to be produced relatively easily. The result of this is that while there are a minority of future classics (the Blackwell series, some of Daedalic's stuff), the vast majority of indie adventure games are, putting it mildly, utter shite.

That sums it up.

What kind of games were you hoping for ?
RTS are at some kind of dead end. And they need lots of balance (edit : i.e. time, hence money).
FPS are mods, AAA, free to play => very competitive, you need a lot of resources to make a difference (be it ideas, engine, marketting ...)
RPGs take time and people (edit : see rts).

Bottom line : puzzle platformers/rogues/story_driven are short-term & low resources investments that are worth the risk to take as an indie.

There are tons of indie adventures, platforms, puzzle games, RPG's, survival horror, simulations, ...

I'm not at all sure that adventure and platformers are the most common. Point and click adventures are probably way behind RPG's. If (like Desura) you include visual novels and "action adventures", and just anything with a bit of story, then this category probably wins.

Searching for PC games on Kickstarter, I also don't get the feeling that point and click and platformers are the majority of games.

Certainly point and click adventures have had a resurgence on Kickstarter, but I still think that RPG's beat them handily.

I also wondered the same. I guess because two years before there weren't so many and developers thought it would be a gap to fill and also they are easy to produce (and maybe also because you can make them somewhat short and casual). But the collective thinking resulted in abundance of these "unique" or "original" games. You can observe this pattern (herd instinct) very often everywhere. It pays off not always following the mainstream.

I would like to see how many of them actually made a decent profit.

I think it's because there's still the wide misconception that a game NEEDS a "unique" and "original" core mechanic. Haha, yeah, noticed that one already. But generally, "retro" looks are far too popular among indies. I mean, we're at a point where 2D games can have ANY look (due to the high screen resolutions, barely any limitations when it comes to processing speed and memory etc.) and yet... for such original and artistic fellas they are quite dull.

Yup.

I would imagine when Braid and Meat Boy made so much money a ton of half-decent programmers came out of the woods and decided to strike it rich by releasing some random average platformer. Now we're all bored of it and tone them out, and those developers then write passionate blogs about "the death of Steam" or whatever because no one bought their shitty "me too!" game.

Happens all the time.

I think the more informative phrasing of the question would be "Why are so many adventure games and puzzle platformers indie games?"

If you ask me, it is because they're the kind of game that can be personally crafted, and each individual element was personally placed there by the developer.
In an adventure game, each room scene was drawn separately, each object in that room was placed their specifically, and each puzzle was thought up and placed accordingly, and almost every action or inventory use can have a personally crafted response.
In a puzzle platformer, Each level is individually crafted, Each puzzle is placed specifically, and so on.

It is the sort of thing that can't really scale up well. So for example, even in something like a AAA RPG game, you'll have a quest-hub (maybe the local tavern), it'll have a list of specific quests (token fetch quest, token escort quest, token kill x-number of y-creature quest", etc). They can't do something significantly different, because that'll require a whole new number of art and sound assets and so on, something that doesn't bother indie devs as much (since their games are on a smaller scale).