In general a higher bill is a proxy for a larger meal of more people in a more high-end establishment so it tracks well.

I agree if you had the $200 sea food tower by yourself it deviates from that otherwise perfect proxy. But that's already a weird situation so just pay the tip and move on.

It's not a good enough proxy for more people. If you compare the least and most costly items on a menu, even adjusting for size, you'll find that there's often a 2x to 4x difference between them. If I pick one over the other I will also have to pay 2x to 4x in tip. That just doesn't checkout.

Also, why do you need a proxy for the number of people when you can just count them? In Europe a service charge is relatively common and it's a per-person fixed charge.

A massive price difference would be the drinks (also the most of the profit) - realistically opening a bottle of expensive wine vs the bog standard cabernet serves as no proxy to anything.

Likely certain single malts vs jim beam.