Financially they were born a few decades early. Today their prime eighties / nineties physiques would generate serious money each year.
Youtube, TikTok, Facebook, Instagram, Twitter, patreon, etc
No need to enter competitions that require extreme risks with regards to conditioning, vascularity, diuretics and such.
It costs a lot of time and has to be done at a professional level, but photos and videos of their eating, training, cars, trucks, girlfriends, house, interiors, holidays...Rory, Berry, Mendenhall, Bob Paris would have been multi millionaires within just a few years.
DeMey may have already been a millionaire. Remember how much he was making with the WBF. He had one of the higher salaries (over $200,000/year, which is probably well over a million by today's numbers).
Plus, some of these YouTubers are taking extreme risks anyway. And everything is relative. Nearly all of the bodybuilders from the 80s and 90s that you praise now were considered "freaks" and "grotesque" in their heyday by the public-at-large....and by their predecessors.
Even back in the day, there were a number of "amateur" bodybuilders, who made more than IFBB pros due to marketing. Shows like American Muscle, Muscle Sport USA, American Gladiators, and the magazines did for them what TikTox, YouTube, Facebook, and Twitter do for today's bodybuilders.
Remember Frank Sepe, Mike O'Hearn, Joe Bucci, Dennis Newman, Paul DeMayo, Skip LaCour, Chris Sare, Erika Andersch, Raye "Zap" Hollitt, etc.
They got lots of press and quite a bit of coin, despite never turning pro (or turning pro and doing little afterwards).