Why would a wrestler choose to lose since the bigger stars make more money?
For the same reason that an actor agrees to get clipped by Tony Soprano. It is what the script calls for and they are professional. If a wrestler decided to go into business for himself, he would find himself unemployed very quickly.
Do the wrestlers get hurt?
The art form that wrestlers participate in is very dangerous and has even resulted in death for those that have made a mistake in the ring. While a WWE wrestler would never intentionally hurt his opponent, accidents do happen. It is very rare for any wrestler to end their career without suffering a major injury at one point in their career. However, sometimes the physical nature of the sport allows the writers to create a fake injury.