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It would instantly tank a lot of huge apps/industries. Especially ones with razor thin margins already.

Consider stock trading apps/fees, for one random example at the top of my head.

It would be more like rent is free if you're unemployed, otherwise x% of your income.

It doesn't work for both the same reason as the example. Everyone who would be advantaged would leave to the one which doesn't charge fees based on something irrelevant to operation.