Depends on the game, some games have everything on steam workshop just because it's already integrated into the game and faster to set up mods (Cities Skylines, Space Engineers, etc.). Has nothing to do with it being casual.
How horrible they earn money with stuff that is basically harmless and has no influence on games. As for crappy games/early access, that's up to the fucking buyer to figure if its worth purchasing.
right it absolutely depends on the game, but since they have started with skyrim, and no other games yet, im using it as the prime example. You simply cant mod large portions of skyrim using steam, or rather you can, but you are taking the hard road. So, yes, its the casual one or two mods that makes it much more vanilla and casual then say adding hundreds. Im sure this same concept is added into any other game you included up there, you dont completely change every aspect of the game, you just flavor it with mods, hence thats pretty casual.
-Theyve created a paywall for using mods
-The modders are earning money, yet still not responsible for their product, similar to early access products
-Ive never heard modders state, "i mod for money", its always been a hobby/side thing, sure making cash is great, except, they arent making nearly any of it at all, 25% revenue......come on(this is why it shouldnt be supported)
-steam is influential, if they can get away with it, then it sets precedence for more to come, greedy monetization, everyone crucifies EA for it, but wont cuz steam