@reddog21 10 minutes fewer boarding can add another run for the plane by the end of the day. That's a significant amount of revenue. The practice dates back to when SW was an intra Texas airline and carries on now more out of tradition.
The number of WGA or WGA+ fares is a sliding scale depending on what they think they can sell. If they thought they could sell 160 full fare anytime tickets, that's all they would sell. When they aren't sure, that's when you see the sky high release day fares and no WGA. Then they'll assess demand and open the lower fare buckets.