I'm certainly not arguing that many climbers are making $1 million/year from sponsorships, but I do think some are, or occasionally do anyway.
One of the interesting things about climbing though, is that this is often all the compensation climbers get. There aren't climbing leagues/teams that pay climbers a salary comparable to other sports (I suspect some competition climbers get paid a salary or stipend, but I doubt it's as much as a professional football/basketball player). But there is so much money to be made from selling climbing equipment, the manufacturers are heavily incentivized to get their names out. And the superstar climbers like Honnold will get sponsorships from other companies as well (Red Bull, Clif Bar, etc.)
I think the intended list of 'who would be making those millions' is limited to maybe 5 people (eg: Alex Honnold or Adam Ondra), not the hundreds who call themselves 'pro climbers' (ranging from the top echelon of rock and competition climbers to dirtbags getting a discount on shoes).
One of the interesting things about climbing though, is that this is often all the compensation climbers get. There aren't climbing leagues/teams that pay climbers a salary comparable to other sports (I suspect some competition climbers get paid a salary or stipend, but I doubt it's as much as a professional football/basketball player). But there is so much money to be made from selling climbing equipment, the manufacturers are heavily incentivized to get their names out. And the superstar climbers like Honnold will get sponsorships from other companies as well (Red Bull, Clif Bar, etc.)