His ratings are amongst the highest on cable tv. His style both attracts viewers and turns off others. The only person on earth I can think of that would pull a larger tv audience in that time slot would be Limbaugh. Whoever takes the slot will be lucky to pull 50% of the audience.
Remember, Limbaugh was a total failure on television. Even back when he was funny, his spiel played to a radio audience, and not television.
And he’s even losing the former, now. (I haven’t listened to him in a long while, so I can’t speculate or address the possible reasons.)