Lazy people prefer having one bank for everything. Savings, mortgage, credit card, investments. The way you get all that business is by having better pricing and/or a more polished app than the competition. If people want envelope budgeting (and I don't claim to know whether that's the case) then you should probably implement it.

The money in it is that it makes you more likely to deposit with that bank which gives them the reserves to legally lend out money, like in credit cards, which is how they make money.

A consumer bank is dependent on its deposit base.

I always thought the money was in the float for them. The more money they convince you not to spend and just hold onto in your account, the more float they have to make money off.