Doesn't Steam allow indie developers to generate as many keys as they want for free? The Humble Bundle gave me a lot of Steam keys the last time I bought something from them and Steam didn't get a 30% cut from it.

They can’t exist solely off Steam, but selling on Steam + GOG + maybe even directly is better than exclusively Steam.

I know I’m in the minority, but especially indie titles I try to buy somewhere else and look for a direct sale, GOG, and itch.io first

Indies don't earn enough for it to matter. The cut only matters for successful companies so nobody is complaining in the end.

If your game sucks then it doesn't matter because 30% of nothing is still just nothing. If your game is good enough then you get a discount.