Citation needed. For riots, it's obviously wrong: football hooligans have been doing it for ages, and they have no underlying cause but "let's fuck shit up".
For demonstrations: it's mostly a social thing. If your friends go, you go, because otherwise you're signalling to your friends that you are not like them, and you don't want to do that, because being isolated hurts.
Only if you aren't invested in the cause. Not everyone takes a nihilistic nothing-matters approach to this sort of thing.
Most of them don't want that more than they want to stay dry though, so bad weather usually translates into smaller events.
What if someone is there for more than one reason(Hint everyone)? Do they not count anymore?
Bad weather lowers attendance for all events you dullard that doesn't support anything you've said. You're just ascribing intention to thousands of people and it's really lazy thiking. You haven't even scratched the surface of why some people are there but go ahead and keep making your wild assumptions