Muzan was screaming at you and the other Uppermoon's because he was stressed out from not being able to find the blue spider lily he needs to conquer the sun and he yelled at you specifically because in his eyes you do the least amount of work

"AND YOU! WHAT DO YOU EVEN DO TO SERVE ME?! YOUR PATHETIC AND DON'T DESERVE TO BE CALLED AN UPPERMOON!!!"

you kneeled there silently accepting his yelling since you deal with it a lot and so therefore doesn't effect you