Yeah, this is one of those things that struck me as a little odd when I first got a dog, but our dog does enjoy his crate. We have a 7-year-old 80lb pit bull, and I was advised by dog trainers to crate train him. So we did do that for the first few months/year. It was originally for house training purposes, and also for keeping him out of the way when we needed to (like when company came over.) We never used it as punishment, and he responds instantly to the “go to bed!” command we have to go to the crate.
Anyhow, these days, I only send him to the crate maybe once every two weeks (when the cleaning lady comes over.) But otherwise, I leave it open, and I find him sleeping in it several times a week. It’s clearly one of his three or four preferred spots in the house.
We do lock them in. Always have since they were puppies. I’m not sure what they’d do if we took the doors off. They’re good with it, so I’m not changing anything!
My dog loathed his crate. He NEVER went in on his own, and would whine and jump up and down as a puppy wanting to get out.
I never left him in there all day. I worked from home so it wasn’t an issue. He’d have hated it.
It was useful to housetrain him at night, but once he knew where to pee, he was free of the crate, allowed to roam around the house and 100% happier for it. He never gave the crate a backward glance and we sold it at a carboot sale.
I don’t generally have an issue with crate training, it clearly suits some dogs. But it doesn’t suit all, and should be used appropriately as a result.