To all or a specific part?
I guess I'll adress 1&2 by saying because it's a competitive event with a very limited time frame, but primarily because it's a competitive event.
The only reasons anyone should be allowed to transfer from one corps to another within the same season (provided they have an open spot, of course) are: abuse, discrimination, harassment, ect.
For #3, I don't like the fact that someone can come in the last couple of days and recieve the same recognition and praise as the other members. In a way, it's disingenuous to those who have put so much of their time and effort with the corps.