Not totally sure but my guess is that the west side is so thick that there is a lot of escapement. A full season on the cows out here on the east side would maybe be to hard on them. Another thought is that they don't want to mess up the spike and big bull hunters and feel that if you hunt good and hard, Wednesday thru Sunday is plenty of time to find a cow in the Yakima and Clockum herds. just some guesses by someone who has wondered the same thing at times. Way out east in the Blues, the cow tags open up on the same day as spikes and I think that is because it is so tough to get even a cow in that massively huge and rough country that you need the extra days.