What's even more absurd: Consider ordering a bottle of wine for $30 vs. a bottle of wine for $300. The waiter has to do the exact same thing but suddenly you are expected to tip $60 instead of $6 if you were satisfied with the experience.
I still think tipping is BS, but higher end restaurants will attract higher skilled front of house, and so it makes sense that they'll be paid more despite doing the same thing.
That's the same stupid reason why we have a dog tax in Germany. Some centuries ago some king - just on impulse - decided "if people can feed a dog they surely must have some extra money to give to their king". And we have to pay that stupid tax even today.