I think I recall over the years a number of complaints or at least observations about the costs (time, money, etc.) of road trips to Seattle compared to any other MLB city. One of the obstacles Portland would have to overcome is a similar degree of remoteness.
I imagine the Vancouver Grizzlies had a similar problem, especially with three of the teams in their 7-team division being in Texas. Add in Minneapolis, Salt Lake City and Denver, and that's a lot of long road trips. Same for the Sonics (until they moved) and the Trail Blazers.