I suspect that this is simply poor IT compounded by poor ability to handle simple enroute misconnects. Indeed WN ought to rebook onto the next available flight and the 7:30 had availability.
Given that there is no such thing as BS, it is simply a boarding position, all WN needs to do is rebook into the same fare basis (the terminology is just cutsie marketing) and OP then boards the 7:30 at whatever position he ought to have.
What WN apparently is not able to deal with is the fact that OP had internet connectivity so although his original segment had pushed from the gate, he was able to handle rebooking himself.
OP clearly has issues with WN. Time and again.
I am no WN fan. It fills a small niche when there is nothing else available. But, OP's profile does not list his home airport and he lists his destination only as "HOME" so nobody here can help on that front. However, PHL-PHX is an AA hub-hub route with assigned seating F and MCE seating and so on. That is an alternative worth considering.