Tips supplement incomes so restaurant owners can pocket the profits that would have gone to paying their staff better.
I hate to defend small restaurant owners because so many of them are complete assholes but they are not exactly Scrooge McDucks dealing with Elon Musk levels of money. Elon Musk could cover the tips of everyone in America.
Oh I didn't mean to imply it was unpleasant, just certainly not as attentive, you'll have to ask for refills on water or spend spend a long time waiting. Though that said in Tokyo the service was on par with New York and they don't have tipping culture either.
In Europe though, the waiters get healthcare and good wages so they have reason to be happy.