Let's call a spade a spade. BYU rugby isn't good because BYU has the best athletes. They are good for the following reasons:

1) Their players usually have WAY more experience playing rugby than other university teams. This is because Utah has a very robust high school rugby program. To put it in perspective, I played rugby in High School outside of Utah. In my school of 4,000 kids, there were about 25 of us who played on the rugby team. There were no try outs, if you wanted to play, you were on the team, if you were an upper-classman, you started.

2) BYU has a large number of international students, especially from countries that play competitive rugby (such as Samoa, New Zealand, Tonga). These are locations where the top athletes play rugby. Again, to go back to my High School experience, if you got cut from the other "traditional" sports but wanted to play some sport in high school, maybe you played Rugby, but only if you couldn't make the golf, tennis, or soccer teams first, and you didn't want to wrestle.

3) Coaching - BYU has been lucky enough to have a phenomenal coach for the last 20+ years in David Smyth. If you couple experienced players with good coaching, you get a good program.

4) Notoriety - with all of BYU's past success in rugby, if you are a good high school rugby player, odds are, playing for BYU sounds very appealing because you know there's a good chance that you'll win a national championship, and that sounds pretty awesome to a high school kid trying to decide where to go to college.

Now compare all that with most other universities who's rugby program is made up of guys who try out rugby because they hear that it's fun and the players all go get smashed after their matches.