Why is the game updated so frequently? Is it love of the game, player exploits, fine tuning and balancing or something else entirely?
All of the above, really.
If a unit is universally loathed as useless, we want to make it more useful.
If a unit/strategy is letting people bypass so much challenge that they're having less fun, we want to rebalance it so that it doesn't short-circuit the game.
If a particular bug (or feature) is causing lots of player annoyance, anguish, etc, then we generally want to make it less painful.
If I'm feeling like making the hybrids do something really dangerous, well...
And there's various degrees of all that. Mostly the current work is towards refinement of what was there in 5.0 and taking advantage of some relatively gentle iteration with player feedback while we're focused on AVWW. Some of it is new stuff, because a little new stuff is fun.
Its kind of hard to keep track of things as they pass by with changes from patch to patch.
You'd probably have been horrified to see the times we're actually working seriously on AIW
Only one patch a week? Hah.
But we don't/can't keep the really high-speed stuff up for long, it wears everyone (us and y'all) out. But what's going on right now is pretty sedate.