If you pay off your balance every month, there is no interest accrual. For my wife and I, we put pretty much everything in one card, pay it off, then use those point to fly for free on vacations. It's saved is thousands of dollars on travel that we'd still have gone on, but had to pay for. I have a buddy that plays the system and maximizes points and other CC perks, but that's more work than I'm willing to put into it.

I also understand not wanting to use CCs, so no judgement here, just responding to your, "why".