Even if the store requiring proof-of-insurance request is reasonable..why would their risk be any different if the drinks were bought at their store than if they were donated?

I understand the practicality of whoever's building/property is being used wanting to make sure their place is being used by someone who has adequate coverage.
I think it's absurd for the store to ask for proof and I can't see any logic in it unless it was part of their weeding process. It seems like they were asking for information that's none of their business.

If they can't donate drinks, why would it be safe to sell drinks to the organizers?
It's the same drinks and the same event.