otter wrote: but by law, I believe they have to ask your income (although they can go by the initial app income within the first twelve months I've heard).
They're required to consider your ability to repay. (Believe it or not, that was not requirement of extending credit before the 2008 banking crisis.) The simplest way of doing that is asking your income. They can, if they care to, use other means, like, for instance, your history of deposits in other accounts they hold. Typically they also ask for housing cost, because that's the biggest chunk of most people's budgets, and it's relatively fixed.