Valve works like this: the employees pick what they want to work on. Nobody wanted to work on HL3, so it got cancelled. When the people who actually want to work on it start it, the work on it will resume. You just need to be patient.
WHAT SHOULD WE DO NEXT IN VALVE? WE COULD GIVE OUT MORE CRATES; WE COULD MAKE MORE HATS! WE COULD FIX ALL THE TF2 BUGS; I SHOULD HAVE WORKED FOR ORIGIN! A BIT OF THE BUGS?