The US has to be the only place I've ever visited where tipping is so in-your-face to be honest, but I do kind of feel like that's where a lot of the "appreciated but not required" talk comes from. This forum does seem to have a largely American audience, and everyone knows what tipping culture is like in the states.
In one of your previous posts you put that a tip is, by definition, optional, and whilst that's true, there's no denying American culture has twisted it to be the most mandatory optional thing you have to do haha - I feel like people who say it's "appreciated but not required" really are coming from a place of good will, especially if they're American, because as countless people have said, there is a pressure to leave tips anyway depending on where you're from in the world, so to say they're not required could easily be a sigh of relief to some people.
Not that I'm disagreeing with you or anything - I'm also not from the US so I agree whole-heartedly that it's a weird phrase to come across when tipping is, inherently, completely optional anyway (i.e. it goes without saying they're "appreciated but not required") - but I guess it's important to consider it from other perspectives too.