When I trained back in 2000 the only thing that the flying school used the C152 was to train up to GFPT. After that it was 4 seater A/C due to the fact that the the slower cruise speed of the C152 wasn't really suited to go on longer navs.
I guess flying schools figure its not worth the out lay for a 2 seater when it is only used to train students to GFPT.