common reasons to be silent:
1) keep hometown pressure off the prospect, if he chooses a rival school.
2) the staff wants to make a big splash with an announcement and is delaying it until the timing is right.
3) the prospect wants to continue to hear from other schools, so he doesn't want his current favorite known.
4) the staff is courting other prospects at his position and doesn't want the announcement to scare off another target.
5) the school wants to avoid being negatively recruited against, so they lie down low in the weeds.
6) the school has landed a sleeper prospect and they know with a public announcement, it will raise his profile, thus bringing on new suitors.
there are plenty of other reasons as Larry can tell you.