Ed...

Chris and Claire quit saving the world since Umbrella went down, thus no need for an anti-Umbrella organisation.

Barry went back to his family to live happily ever after.

HUNK only ever appears in mini-games.

Leon is working for the government on protecting the president and his family.

Sherry was taken in by the government too.

Jill stated that it was her "last escape" in RE3.

And Steve is just...well, Steve is DEAD.

EDIT : Well, since Wesker has every damned virus ever made, the plagas sample, and god knows what else, you know that he has to make his move eventually, and Ada will be by his side.