It’s smart to make borrowing harder, they have no data to base lending decisions on.
Your credit record has no relevance to a bank, big banks base decisions on many factors your credit record is only one of them. With a new bank they have no historical data, they don’t know there profile of customers, so have no idea what lending entails. Every single bank is different. For example if I log into my barclays account there is a whole pre-approved section, based on my account, all banks do the same, some make it public like barclays, some do not, but that is why you can walk into a branch, and they can tell you straight away if you can get a loan or overdraft, or they will say they will need to run checks.
Over time Starling with have the data, they will adapt and change, but at the start they are doing what they should be doing, and that is being very conservative. They will also agreed to act like that, during its banking licence application.