Its not free, someone else paid for your little "bonus".
Its not a good road to be on. Credit cards are a slippery road, with pitfalls and dangers all around. If your a safe driver that pays attention, then you can probably drive the road just fine.
But if your the type of driver that does not pay steady attention to the road, there are all kinds of potholes and other dangers.
Having to keep track of a credit card, when its bill is due, and how much I need to pay is nothing I want to bother with. So what if I make $50 cash back, its not worth the hassle to me.
My wife and I keep some cash put back for emergencies, which is separate from our savings account.