20% has actually been the norm for a while. Maybe it was a bit on the upper end a couple decades ago while now it's more default, but I remember my parents tipping 20% for normal service back in the 90's. Of course, with prices soaring tipping is still getting pricier and pricier, but the expected percentage here has been relatively stable.

The thing that's out of control is where you're expected to tip now. I often see a tip prompt come up at retail stores where the only service the employee provided was ringing up the items I brought. I never tip in those kinds of situations, and I doubt the employee would see any of it even if I did.