There's definitely a psychological component, and it's also partially an attitude thing.
But like hillerby said, there can be more issues at a wedding, with potential expectations from many parties. I once showed up at noon to shoot 1pm formals for a 4:00pm wedding. The entire wedding party was already ripped. Parents, too, LOL. Then when we went to the pre-approved outdoor location for shots, some of the bridesmaids were all annoyed and whiny that I wanted them to walk through some prairie grass. This was all approved in advance, mind you.
Some people are really easy-going and good at dealing with obnoxious and whiny people. I'm not. Well, on the surface my patience has never broke in these cases, but it was on the verge, and I wanted to quite before I would up getting sued for lodging an SB-800 in someone's rectum.
A wedding is also a big deal for a lot of people; an important day. Most of them have no idea they'll be slogging through a bitter and painful divorce within a few years. LOL. Anyway, it's important, and there are no re-dos, so that adds to the psychology of stress.
Eventually I decided I didn't want to do them, but instead of formally quitting, I kept raising my price, thinking there was some level at which people would quit booking, and some level at which I would say it was worth it. I didn't reach either. After someone booked when I offhandedly quoted them $4000, and I still thought I was dealing with too much for that money, I just quit. Last year someone offered me $8000 for an all day wedding and I turned it down with no hesitation.