The WIAA doesn't look at that stuff for most sports, including wrestling. They only look at number of teams (for allocations) and trying to keep teams in their "region" the best they can with equal numbers. When there is a big disparity in number of teams, some leagues will have to cross the mountains for regionals but not often.
4a boys - GSL goes with KingCo so each region has around 13 teams so they are get 4 berths to state. If GSL stayed in eastern washington with Big 9 and MCC they could get 5 berths and KingCo only 3 so WIAA evened it out.
Girls 3a/4a - If WIAA gave region 4 a league from region 1, then all regions would get 5 berths to state. As it stands region gets 6 region 2 & 3 get 5 and region 4 gets 4.
I've found that most of the time, WIAA won't send a westside league across the mountains unless it's pretty much their only choice.