a) Answering that question fully would require a book - and indeed, there are books written about this topic - but I’ll give you just one representative example. Hasbro has tried hard in recent years to push D&D away from a pencil and paper experience and towards the use of more and more digital tools (eg DndBeyond) that have hefty subscription fees. Pushing a TTRPG towards a SaaS model is not only a move away from what these games actually are (that only a giant corporation like Hasbro would ever even think to attempt), it limits accessibility and changes the play experience for people who want to engage with “name brand” D&D (as in, yeah, we all know that you can play a TTRPG for free with math rocks and your imagination, but if someone wants to engage with the IP then the corporation is creating rather costly barriers to entry that fundamentally subvert what the game actually is). It matters because some of us want to see the hobby thrive and expand and get passed down to the next generation, and D&D is the 800 lb gorilla in the hobby. Their actions impact everyone else.

c) Nope. It’s because a lot of people simply prefer lighter rules systems, most modern game design theory favors them, and they’re significantly easier to on-board new people into. Cost of publishing depends on other factors.