The internet is a place where millions of people are all competing to get famous and make it big. If the internet doesn't like something they'll say it straight to your face. If you can't constantly put out content then you'll sink and people will flock to new people. Someone who was a pioneer of Twitch should understand that.
The thing is that he lucked into it. He was a decently charismatic guy who was good at what he was doing, and jumped on the train early, but he really didn't have anything that was unique to him specifically (and few of the internet-famous people really do). It's interesting to contrast Cosmo with Siglemic, a Mario 64-speedrunner who became gigantic way back.
Siglemic said repeatedly that he didn't want to be famous and longed for the days when his stream chat was small and personal, so eventually he stopped streaming regularly or started streaming content that had nothing to do with Mario 64 in order to drive people away to people who still would speedrun Mario 64, which he did. He knew that the reason people watched him wasn't his personality, but his skill, so he avoided showcasing it to make people go somewhere else. He still streams now and again, and has the small chat that he always wanted, with his prior success being nothing more than an internet footnote.
Cosmo did the very same thing, except that was never his intention. He actually believed that people were obsessed with him and not his prowess in Zelda, and that no matter how hard he abused people, left for long stretches and started streaming absolutely insane ramblings, that he was untouchable and everyone would be his paypig for ever. Of course, anyone with a lick of sense knew that wasn't the case, and now he's desperate to regain his former status.
As hard as it may be to become famous to begin with, it's much harder to regain it after you've lost it. Cosmo is in the absolute worst position to become an internet personality, and not just the footnote of tragedy he currently is, and it's all his own fault.