My theory is that players are moving up in stakes for certain tables.

In most of the 20-50bb games the table vpip was > 30 and sometimes > 40
I have tons of notes on tons of players at 10NL and at most of these tables I have no notes or hands.

The 100-250bb tables seem to have more regs and a couple of fish. I found one of these tables last night with 6 regs and 3 players with >65 vpip with one of those playing 85 vpip.

My theory is the regs are playing 40-100bb and 100-250bb tables and the 20-50bb tables come from lower limit players.