It has a certain logic to it, and I think US tipping culture basically follows the same rules.
Even if you almost always end up paying the bill + 20% tip, Americans like the idea that they could not pay the tip if the service was bad.
The appearance of free action is appealing and preferable to being forced to pay the extra amount, even if you almost always pay the amount willingly anyway.
In my experience, everyone who defends tipping culture is defending not paying the tip. I don't buy this idea that someone likes tipping culture and still pays it. After all, you're free to tip anyone you want regardless of culture.
The problem is it is so ingrained in US culture that switching to tip-free has generally failed where tried, even in pro-labor lefty hoods in blue cities.
Numerous restaurants in NYC tried and flipped back over the last 10 years. Restauranteurs reported illogical / innumerate behavior where sales went down when they switched to untipped higher prices.
https://www.eater.com/21398973/restaurant-no-tipping-movemen...
The only restaurants that it stuck were Japanese restaurants that cater primarily to Japanese ex-pats, because culturally its familiar to them.
Well sure, it has to be mandated through law or underpaying workers will inevitably outcompete those that pay workers. I don't think that's an argument that anyone likes tipping culture (except wait staff in bougie cities).