My guesses for plausible reasons are:
1. They want to rest their top guys/not overrace them, and since their team has so much depth, they have that option.
2. They wanted to give more of their runners a chance to prove they can be in the top 7, in case someone who hadn't raced well had a breakout race this time around, they could cycle him in in the future.
3. They want their top guys to race in the Trials, and this is tied into that somehow.
4. They wanted to give some of their slower runners another race for experience/ a final race if they were a senior.
5. A mix of any or all of the above
It's not often that a team can sit out their top guys at conference and still almost win, I'd bet they're confident they can win NCAAs and want Grijalva and Young to be prepared to race for the win.