What are the artistic reasons to shoot "Curb Your Enthusiasm" in a higher frame rate?
It gives me the impress I am watching an old show.
It looks like an old soap opera?
You're actually referring to a change in Frame Resolution not frame rate, increased frame rate is that horribly obnoxious thing they did with some versions of The Hobbit, made it look like a video game cut scene.
To answer your question though, the reason why they did change from 480i to 1080i is simply because of the demand and pressure for it, with most other programs offering 1080i to their customers, to not do it would be to fall behind.
However, there might be a setting somewhere in your tv to adjust motion blur. Turn it down, that might help.
I'm watching season 1 in 1080p form. I'm not sure if it's remastered or something else but I also notice it looks differently from other old shows that are properly made into 1080p (like Cheers or Friends).
I've been able to find some info on how it was shot. In particular, they used DigiBeta cams which were commonly used in the field, but not necessarily in studios (i.e. where most of those other shows would be shot).
From what I found (John Pytlak on film-tech.com) (emphasis mine):
Unlike the special, where David acknowledged the camera, the camera and crew are never acknowledged on the series. "Curb" is shot on two DigiBeta cameras and has a 20:1 shooting ratio, giving the editors a whopping 10 hours of footage per episode, on average. The show started production in March and is just now finishing its initial order of 10 episodes. On average, it takes about a month to cut one episode."
I think those two factors play a role in getting the look you refer to. You might compare it to some news footage shot 'in the field' (in the same era) where they'd use similar cameras.