When they choose to go in, the door is open yes, but the point is even though they are put in there with the door closed sometimes it’s still where they usually choose to go when it is a choice.
It’s definitely the crate they like btw, and not just because there’s a bed in it.
My last dog was crate trained as a puppy and then had operations that needed crate rest and because of those developed behavioural issues that meant he had to be crated to allow strangers in the house. So as an adult he was crated by me much more than I usually would do.
It was still his favourite place to sleep when he had other options though, it was where he ran to if something in the garden scared him (bog standard garden, but apparently hedgehogs are terrifying). It was where he snuck off to with his stolen socks.
But also, when we swapped out the large size crate for a XXl - even though I’d put it up and moved his actual bed into it he spent a good 15 minutes trying to work out how to get in his old folded up one. When we went on holiday with him, he wasn’t interested in the bed until we got the crate out and put it in... that’s when he’d settle down.
Do some people not crate train properly and just lock up a stressed dog? Yes, I’m sure they do, but then I’m very sure there are owners who don’t use crates that also do things that aren’t ok.
If you go by the objections some people have about crates, you could assume that some dog owners don’t let them have choices of beds, leave 8 week old puppies alone overnight and leave their dog home alone for very long periods of time - because why would you assume that’s how crates are used unless that’s how you think people look after a dog? I’m not entirely serious, obviously, but... it is weird that people have strong feelings about it when they’re making wrong assumptions about how most people use them.
They’re absolutely not an essential, but they are generally a positive thing.