This has happened every year Ive hunted bears. They decrease activity at my bait sites drastically the last week before the season. Usually not totally, but often times just showing up in the middle of the night or whatever. I've always attributed it to other guys not only putting baits out last minute that attracts them away from mine, but just added activity in the woods in general. Guys putting up stands last minute, scouting last minute, dragging in baits etc. I think the increased pressure chases alot of them off.