According to Inside Social Games, the driving force behind these closures was low traffic. The games are pretty old compared to most social games, but it's surprising that the strength of the IPs didn't help them stay afloat longer. Don't people still love Pac-Man? Is Taizo Hori of Dig Dug fame doomed to a life of obscurity? Perish the thought.
In any case, the games will remain playable until March 19th. If you've never played them, or feel the urge to give them one last go, it's now or never.
Goodnight, sweet princes.