I do exactly what you do. I got the highest percentage cash back credit cards I could find. Then I started charging everything I could on the cards and set my bank account to pay the cards off in full every month. I just reap the cash back at no cost to myself.
The rewards aren’t huge, but if I can save 2-3% on my expenses, why wouldn’t I do that?
At this point I've made hundreds of dollars from the CC companies and haven't paid them a dime in interest.