Because most people in the US don’t know who “Andrew Windsor” is but have heard of “Prince Andrew.”
Did his titles grant him any powers or privileges that he doesn't retain? What's different for him now?
A large amount he's lost is also ceremonial, it sounds like he won't be removed from the line of succession cause that would require approval from all the separate countries the monarchy reigns over to do so (and he's like eighth in line so extremely unlikely given his age).
He's been excluded from a lot of official events already so a lot of it is just making it official.
He's still not being criminally charged with anything from the government.
[1] https://erskinemay.parliament.uk/section/4571/lords-privileg...
Why?
In this country there's still loads of people who buy into the whole majestic nonsense of the royals. I was talking to my mother the other day who was saying how my grandmother was having a big rant about how they couldn't strip him of his titles as they're his birthright and how hard his mother, who protected him, worked etc.