Some kid getting pocket money from a lemonade stand is significantly different to accepting recurring donations as an adult. Dealing with either setting up some sort of non-profit, managing tax in your country, accepting international currencies or supporting largely unethical/hostile US based financial institutions like Paypal, it can be a rabbit hole that some just can't be bothered with.
It's also just really weird to critisise people for wanting their users to donate to worthy causes.