I don't want to seem mean or rude, but what's the point of this exactly?
We could talk about id Software abandoning DOOM 3? No? Or what about Bethesda Softworks barely fixing their games and letting the community do most of the work through modifications? Oh, what about BioWare releasing only two DLCs for ME1 and releasing perhaps too many for ME2, or what about them abandoning regular updates on the Cerberus Network? Hmmm, let me think (isn't really hard so far), what about Relic abandoning Company of Heroes?
Some exaggeration put aside, can we just look further and realize that it happened regularly before, and continues to happen regularly nowadays? It's not just Valve, and even if the subject wasn't meant to only point at Valve the point still stands, what the heck is the point of discussing game developers seemingly "abandoning" some or most of their games. Heck we might as well talk about SEGA abandoning the hardware market (no please, let's not).