My point in player selection (Try outs practices on a team) is that the playing field needs to be level. For 13 / 14U I have radical ideas like I don't allow one player to pitch on a 54' mound and have another pitching at 60' and try to compare them as equal. We require players to supply BBCOR bats and inspect to assure that is what they are using in tryouts. For team selection an equal playing field is important. When it comes to tournaments I feel the same way, keep the playing field even.
If you sign your team up for a tournament that does not have BBCOR restrictions allow them to use what everyone else is using. If you don't want them using non-BBCOR bats be careful the tournaments and leagues you enter them into have appropriate equipment rule.
There is a great deal more difference between a drop 5 and a BBCOR than just the 2 Oz weight difference. The drop 5 bats are allowed to provide rebound rates that the BBCOR was specifically intended to remove from the game at more advanced levels. In addition if you are concerned about the 2oz they can get a non-BBCOR drop 3. They are becoming harder and harder to find but they are still out there.
The answer to the why to use the non-BBCOR bat if allowed is not difficult, the ball leaves that bat at a higher velocity and travels further with the same swing and contact. I do not have the stats but the eyeball test says up to 15% further with the same swing. If a 13U or 14U freshman player is playing in a summer tournament that allows non-BBCOR bat my thought would be why would they or their parent place themselves and their team at a significant disadvantage giving up 10, 20 or 30 feet on every solid contact by swinging a BBCOR when everyone else is using a legal bat that produces better results?