Well, it's no less weird that store running a promotion saying 'If you buy item X today, we will donate one dollar of the proceeds to charity Y.'
Also not more weird than the British charity thing of "I'm shaving off all my hair, and that's why you should donate to charity Y." (I suspect Brits need an excuse before they are mentally allowed to do something silly. But any excuse will do.)
I've always been baffled by the British charity thing: You want to ride your tricycle from John O'Groats to Ffestiniog? Fine, do it. You want me to donate to this charity? OK, maybe I'll do it. I just don't see the connection between the two. Please explain the connection to me. You don't actually want to ride your tricycle? But if I donate to some third party, you're going to do something you hate? So you're saying I want you to suffer? I'd rather donate if it doesn't cause unnecessary suffering.
It's something we've been raised to do from a young age.
I've never thought about it before, but I suppose it's a way for you to provide some commitment from yourself as a condition for those you're crowdsourcing donations from.
If you don't deliver on your part, they don't have to pay.
When I was in high-school we did everything from shaving our heads, to having your legs waxed in front of the whole (boys) school.
I raised thousands of £ for charity this way, more than I could ever raise by myself at that age.
I'm sure I've seen dunk tanks (throw a baseball, hit the target, person falls in) in plenty of US movies though no idea how common that is in reality.
Regardless, one of the nice things about the practice is does mean people are at least somewhat committed to a cause they are raising funds for before they go soliciting. It also deals with the irrational part of the human psyche and moves the action conceptually from the person begging to the person trading which can have an impact on how people perceive it.
The charity you’re raising for sets up the infrastructure to do the activity. Charities, for example, have spots in marathons which are hard to get other wise.
So if you see a friend is trying to do some personal achievement, and you think the charity is a worthwhile one to donate to; why not combine the two and help your friend achieve their goal whilst also raising money for a good cause.
Also not more weird than the British charity thing of "I'm shaving off all my hair, and that's why you should donate to charity Y." (I suspect Brits need an excuse before they are mentally allowed to do something silly. But any excuse will do.)