This - I'm a photographer and I try to avoid doing weddings, even though they pay more, because of the sheer stress involved.

Not just that, but the expectations are almost always significantly higher (and, in return, the effort that you as a consumer get from those vendors should also be higher.) Speaking from the position of someone who supplies the cake industry, for example, you're not just getting "a cake". You're getting a multi-tier work of edible art that took that cake decorator four times longer to make, requires a special setup for transportation, and usually requires another half hour to an hour of the decorator's time to fully set up once on site. Any old cake could feed 100 people, sure, but do you really want pictures of a flat single layer cake decorated with ugly, mushy balloons half-assedly piped on by the resident 18 year old at your grocery store, transported in a flimsy cardstock box in Aunt Hester's 1970 woody wagon so that half the icing is stuck on the top of the box? If you do, great! You can save a lot of money that way, for sure. But most people want a 3-4 tier cake, decorated immaculately with flawless buttercream and covered in flowers. That shit requires effort, and effort means money.