I wonder what the cause of the mutual slide-off was. Was it just cable existing?
Well, if both shows' clearance percentages were slipping, that would've caused their share points to fall as well (My CBS station growing up in Louisville never cleared PYL for starters, but the NBC one ran $ale in its correct time slot). By this time, the networks were struggling to maintain 80% affiliate clearances for any show not named Wheel of Fortune, TPIR, or a soap.