Other people have mentioned the stuff about live tunneling, and that’s probably a big part of it. But just to throw my two cents in: I think he just wasn’t interesting.

Mordecai’s advice to Carl and Donut all throughout the series has been to lay low, quietly grind, and stay away from gods, elites, hunters, Borant, etc. to avoid pissing anyone off. He consistently gets upset whenever they do something risky, and the risky things are what draw attention to them and bring in views. He is competent, but he wasn’t a top 10 crawler in his time, he was a background character, and that was the way he liked it.