All SEALs receive the same initial training. When they go to their assigned teams training continues. The longer you have been a SEAL the more training/experience you have. My guess would be that a potentially high profile mission like this that the team members for this mission were hand picked based on experience and availability. SEAL team 6 is stationed out of Ford Island, Pearl Harbor. All SEALs, like any member of the Armed Forces, are not always immediately available. They do take leave to be with family who may be stateside, illness, injury, etc.
"Never forget that everything Hitler did in Germany was legal. Never forget that everything the Founding Fathers did was not." Martin Luther King, Jr.