I say this to you every time you get the hump that charity shops have policies.
You always need to check in advance. Not every shop takes everything.
Checking and pricing. Not every shop will be able to check and price every possible thing they could sell so they select what they know they can work with.
Storage. This is the real one. Every shop has limited space and many many many more things donated that it can ever put out or sell. Yes, they want donations all the time but, no, that doesn't mean they can take everything and then, TARDIS like, keep it until there is space to display and it will then sell.
The ones I am aware of end up landfilling a lot of stuff even though they never want to.
That said, if they were rude to you then that isn't right either.