I don't know of any popular game that didn't have DRM and didn't have very strict IP implications on fan content (say, after the early 90s maybe?). It's not like the teams behind the original DOTA or CS or TF ever made money selling those, and would have likely been blocked even if they tried.
It's true though that live service games are quite antithetical to modding because of their need to control player progression and sell it.
Still, I would say the divide between games which supported modding and games that didn't has always existed, with much fewer games in the first category, and there are still huge games coming out today that do. It's even become possible to create mods for console games, so it's not all doom and gloom.