It actually makes sense. People on holidays spend more freely. It's holiday after all. They spend more on restaurants, they spend more on impulsive purchases.
Regarding hiring a professional photographer, probably most of those persons maybe wouldn't hire a photographer for some portrait to pass to posterity while they are at home. It's not just money, it's busy life, other things to do, a portrait might be something that is always postponed. While on holiday they might think that it is the nice occasion to have some properly made "portraits" of them with their children during a pleasant and "different" moment of their life.
A single session of this kind really ticks more than one box: it's a recollection of your holiday and is a portrait of your family in that time of your family history. For tourists with income in the upper 5% it could be a no-brainer. They'll just save something on shopping for not needed things.
Some people just don't know how to spend money and this is a very valid way to spend it.