I guess they're just not good enough.
I know lots of Pakistanis who play football, but they only seem to play 5 a side matches with friends, or in small 5 a side leagues.
I play with some of them and I know they do like football.
Also maybe some don't want to join teams with non-muslims because they know a lot of players will go out drinking, etc. and they won't be able to take part in it so they might feel left out.
Just a guess