NPR reports.

It’s not the way it always goes, but it shows the risk of seeking a new rule. You may end up with a reinforcement of the old rule. More precisely, it shows the risk of ending the enforcement of an informal practice. It led to the formalization of the old practice into an official rule.
In this case, the change that backfired was all about accommodating one person, John Fetterman, a man with mental problems — he was recently hospitalized for depression. It is, it seems, especially important to him to wear hoodies and gym shorts, and what is the big deal? Let the unfortunate man have what he seems somehow to need. 
But he’s in one party, and there’s the other party, and it was a ripe opportunity to drag out the age-old argument: What if everybody did that? And we easily picture the Senate full of unlovable oldsters dressed as if they’re about to attend a backyard barbecue. Can’t have that. And so, John Fetterman must be forced into a suit and tie, at whatever cost to his fragile mind.
They even resorted to teasing him, calling the new rule “The SHORTS Act” (for “SHow Our Respect To the Senate”). That resolution was introduced by Mitt Romney (along with Joe Manchin). Mitt Romney, teasing a man with mental problems? Fetterman still has the option of standing in the doorway in his hoodie and shorts and participating without entering the room.
Good thing they got that done… as a symbol of all the things they haven’t got done.