In my diocese, you can go to some nice, posh, suburban parishes and see folks at mass in jeans, t-shirts, shorts, etc. But if you go down to other parts of the city, into Catholic churches that are mostly African-American, you will see everyone - among the poorest in the city - decked out in their Sunday best - all the ladies in their nice Sunday dresses, men in suits and ties, children in their best clothes.
It’s not specifcally a Protestant vs. Catholic thing, nor a rich vs. poor thing, nor a white vs. black thing. But I think the comfortable parishes could stand to learn a few things from the poor folks on the other side of town. Part of it may be the members of the parish holding each other to high standards.
But let’s not judge people too harshly either… just yesterday, I was travelling back from my parents’ house, normally a 6-hour drive. But due to extensive road construction and heavy traffic, I was delayed by about 90 minutes. So instead of going home, changing, etc as I had planned, I drove straight to church and made it about 15 minutes late for an afternoon mass. I was dressed much more casually than I was comfortable with for Sunday mass. But otherwise I would have missed mass. So on any given Sunday, I don’t know if there may be special circumstances causing someone or other to wear jeans.