If it is a spun main bearing, my bet would be that detonation was occurring, which lead to pre-ignition. No oil can protect from that, it is like a 2T hammer being dropped on the piston as it is rising.I easily ride harder than most people here, so that's my assumption for why the oil went out quicker, besides the weather. Me and my dad are going to take the engine apart and inspect the internals soon. I never really ranlow on oil, I had no leaks. So unless the bike is eating just a bit as well, I'm not sure.
Check the spark plugs for melted deposits (which often look like tiny black glass beads), melted ground electrodes, or even melted aluminum from the piston.