When I was a waitress, I saw much worse (pasta, sauce, & cheese in the carpet and the various sugar, salt, pepper, cheese, and red pepper shakers had someone drip tea or soda into the top with their straw - while bored & waiting for their food - the candles had been filled with straw wrappers, red pepper flakes, and other "gunk"). THAT was a mess.
Crumbs that can be dealt with using a vacuum cleaner or even a carpet sweeper.....what's the fuss? Now, a screaming kid having a melt down? That can start a bad effect of people hearing the screams at lunch and not wanting to come back for dinner - even weeks later. But the "mess" just didn't register as all that bad.