Snapshots aren't updates, but prereleases/beta releases of updates. The only reason snapshots exist are for modders/artists to get a head start on updating their mods/texture packs. Most of the time snapshots aren't even stable enough to run a server with.

In fact Minecraft went like an entire year or so with only an update every couple of months... and most weren't very well received and lacked substantial content(they were bad enough to spawn mods like "Better than wolves"). It wasn't until Jeb was put in charge that updates picked up a bit.