Why the fuck are we having this discussion again? Come on OP, I love GURPS but these threads are getting ridiculous. There are three reasons that basically cover everything.
#1 is this >>64328622
They don't like maths. THIS IS OK. Do not feel bad for being bad at maths. IF you speak english chances are you had a shit maths education anyway.
#2 is they don't have a good GM to introduce them to it, GURPS really benefits from that, if not requires it for some people. Which hey, if you like GURPS so much, why aren't you out there running one shots to introduce people to the game instead of acting like a smug cunt on a Kazakhstani wood-carving board?
#3 is they haven't heard of it, but this thread is such a mess of trolls feeding trolls it's enough to turn off a curious newcomer.