Link for people lazier than me: https://whatisnuclear.com/
I would be fine with paying Reddit for the ability to (tastefully?) promote in my comments
But I think it's not just a cultural shift, but from being burned by everyone hustling for something. People want to drive you to their dropshipping business, their woodworking course, their OF, buy their self-help book or whatever.
They could have easily spent a few hours a week exploring and meaningfully participating in other subreddits that interested them, but they had no desire to spend that time or be a useful part of any community. They just wanted to draw viewers to whatever they were promoting.
As both a user and an advertiser I agree. The communities I visit, if not the whole site, are faithfully anti-ad. But if I answer some questions occasionally somebody will get curious about my profile and check stuff out.