> They've certainly tried and failed

I'm not sure they have tbh, not because they couldn't but because it's not high priority even without regulatory and institutional hurdles to cross. Moving additional pennies around doesn't radically alter the fees banks and credit card providers already get from customers they already market savings products to; a neat little app to start building up savings is an opportunity for investment providers that don't do retail services to gain consumer attention and potentially bigger deposits in the long run though though.