Probably people with not a lot of other options to turn crypto into some more liquid? IIRC most UK banks (including challengers) are completely hostile to anything crypto, so I'm not sure what options one would have.
Not really the case. Some have limits and bans but it is not across the board and many banks don't have restrictions. The issue is the bank is semi-responsible to refund if someone gets scammed and sends money to an exchange and they have been taking huge losses on this; so I imagine some are just blocking it instead.