Cost. The balance of outside customers using WSFCU atms will be so much lower than the number of WSFCU customers using other CU atms. The shared network does not allow positive growth for smaller, out of the way credit unions with rural populations.
Opt for traveler's cheques or taking larger amounts of cash out a trusted out of network atm's fewer times per month if WSFCU bank or atm is not convenient for you.
A salesman's whitepaper on why a Credit Union should join shared branch networks may be a better read:
Is shared branching an expense? The answer is yes, but it should be perceived as an investment with the potential for quickly realized returns. All credit unions participate in shared branching as issuers, meaning they allow their members to visit other locations in the network. Credit unions can also participate as an acquirer, in which case they handle transactions for guest members in some or all of their facilities. As an acquirer, a credit union has the opportunity to generate revenue, or at least offset issuer costs. For issuer-only institutions, providing convenience gives a credit union the opportunity to expand relationships and eventually see financial gains, resulting in real value.