By the sounds of this, you failed the checks they are required to by law - maybe your details didn’t match up. Anti-money laundering is a big issue for banks so they won’t mess around with anyone who might look like they are committing this. Not that you are!
It might be that you have a seriously low score or seriously bad debts (defaults, CCJ’s etc) that might mean a current account isn’t right for you and a basic bank account is the right one for you. This will be up to each bank, and Starling obviously have criteria. I wouldn’t know that part as it’s really between you and the bank.