Reddit is a publicly traded company now so they must have infinite (read: unsustainable) growth to their Shareholders®. This means that what you're seeing now is a trend that's only going to get worse. Their entire app is designed around the infinite scroll of the Meta clones, that's incentivized to show as many ads as they can between posts.
They can probably make it worse, like popup ads when clicking on a thread. If they're trying to chase advertisers to the maximum then it could be as bad as those free mobile games. Maybe that'll make people leave Reddit lol.
Very sad to see lemm.ee shutting down. I liked it here, the instance was easy to pronounce. Good luck lemm.ee admins with your future endeavors.