You know I had this same thought just the other day, and decided to look up some numbers to see just how comparable the situations really are. What I found was that the number of people attempting to cross the US southern border is like four times as many as have tried to cross into Europe, per year. No I didn’t bookmark the source, but you should be able to Google it up like I did. I don’t know why this is a much bigger problem in the US, but it does seem to be.
I was flying home with a snow globe souvenir one day. TSA had to huddle with their team and a calculator to figure out the volume of a sphere on the spot. I don’t know if the volume ended up being under the limit or they just gave up.