Originally Posted by Ragnarok

I think twitch76 's operative word here is "do it on the app or online".

Same-Day Change & Same-Day Standby | Southwest Airlines :
*Customers who book Business Select®, Anytime, and Wanna Get Away Plus™ fares can complete their free same-day change online; Wanna Get Away® fares can be changed online by paying a fare difference. A-List and A-List Preferred Members with a Wanna Get Away fare are eligible for free same-day change, but they must call Customer Service or visit a Southwest Gate Agent to make the confirmed change without paying the fare difference.

So yes. Either it's a intentional extra step to nudge status member to also buy up to WGA+, or it's an missed requirement for IT to build the logic to recognize the status benefit.
Say there is bad weather at a hub, and the call center is swarmed, WGA+ customers may get that last seat you are looking at on the app while you are still waiting for the call to get connected to an agent.