1. Possible, but seems unlikely as the explanation? How many people would read that fine print and care? So many other contracts already have provisions like this and nobody blinks an eye.

2. It need not be against their terms though? They could easily specify hyper-optimized usage in their agreements as something that might result in account closure. This is already done in a lot of other cases; they could do the same here.

3. I don't know about that. Just look at the sheer number of sites that explain how to maximize your credit card rewards/cash back/bonuses. They wouldn't seem to be there if the audience for them was so vanishingly small?

I’m fairly certain that it is not worth their efforts to cancel those accounts, evidenced by the fact that they either don’t do it, or the number of customers it affects is so vanishingly small that neither of us are aware of the practice.

If you believe so strongly that it is worthwhile for them to do this, then perhaps you have an idea for a lucrative career.

But as long as credit card fraud in the US is measured in billions, I’m going to guess that any manpower which can be assigned there is way more lucrative than any manpower assigned to demonizing their honest customers.