Recruiting rankings are based on number of commits multiplied by ranking of commit. Utah's commits typically come on late - they delay many of their commitments until the last minute, so therefore their ranking is always low until it is finalized in February. 

Why they do this is somewhat speculative - I haven't seen a definitive reason, but it seems they "hold out" as long as they can so, perhaps, they can obtain better recruits in case any come along late, and/or they hide their recruiting from other programs that might try to "steal" their commits. 

The latter makes sense ("hide" from other programs) as Utah is the best in the nation at finding "diamonds in the rough" and player development. It would make sense that other programs would try to copy them, and therefore, Utah trying to delay things would prevent other programs from "stealing" their commits.

I am not 100% sure about these reasons, but it seems these are the reasons given by other Ute fans speculating about it.