The age of adtech as the dominant technology revenue model is drawing to a close and Reddit missed out on the golden age. Trying to make ads work now, when it’s clear the future is subscriptions and the like, is just dumb.
Only Google and FB figured out ads, and they were planet-scale companies. Twitter pulled in ad revenue but couldn't make a profit. Reddit's audience is extremely hostile to ads, and they've never managed to attract big advertisers anyway.