My guess would be their ad spend is bad in comparison to the other networks (Google, Facebook, TikTok). Could be because their audience isn't worth as much, could be because the ad formats are bad, could be because they can't get advertisers. But unless they are serving ads from Google's network, my guess is they are 4th place at best.

As noted on other threads, their streaming infrastructure must be a burning dumpster fire of money. Live streaming is super hard since you can't edge cache it, and it requires actual hard computer engineering to make work. If a mere mortal company were to try to run a clone of Twitch on AWS, it would run out of money in days. It also likely uses the same hardware as other high-value products, such as AI.