It's not just temporary fatigue, it's a sense of resignation from an audience that has watched Trump get away with everything, seize back power and embark on his path of retribution and destruction of the things they value. They're mad at how ineffective the institutions they hoped could stop this have been, and they don't want to hear from them anymore.
MSNBC hosts are still on the air talking about the same things they talked about before the election. The audience feels let down by the failure of this messaging and have no confidence in them to make any difference now that the election is over. And Morning Joe's betrayal of taking the show to Mar-a-Lago was the last straw. So they have tuned out.