Probably for the same reason people take snapshots on vacation despite not being professional photographers with thousand dollar lenses. It's a direct connection to the place and the event, a memento. A professional photograph depersonalizes it.
It's absolutely not direct connection. You're looking at the phone which is looking at the thing, not looking at the thing. It's more direct than a professional photograph, but it's less direct than looking at the thing.
> A professional photograph depersonalizes it.
Looking at it through a phone depersonalizes it.
And to elevate oneself socially based on select signalling of goods and services consumed, places visited and activities performed.
The photos will happily sit on a device, external storage or the printed page for occasional review but let's be honest here: it has less worth unless others see it. It's not the memory-trigger aspect that's so important but the feeling people get from knowing others are admiring what they're doing. The act is mostly for signalling.
Some people forget the era where you typically didn't have a camera everywhere you went, and when you did have a camera you were limited by the amount of film you had. I remember that time and have plenty of vivid memories from it thanks to carrying the best camera I've ever owned: my eyes.
the cost to the experience is minimal
For the people capturing the moment perhaps. In Versailles I was whacked in the head with a selfie stick by a pirouetting halfwit. People fumbling with their phones and selfie sticks aren't considerate of the people around them.