I saw that yesterday, their price point is too high for their product. I don't know what Southwest is thinking but they keep trying to make themselves like other airlines but they still don't have the product to match and trying to mimic what other airlines or CCs have doesn't actually mean they would have the product to match, the product in this case is their entire actual airline experience while on the plane like different actual seats (not just talking about leg room), meal service, other amenities while on the plane (other than a drink) all the while charging a lot for the actual ticket.
It would be literally insane to charge $650 for a SWA CC and yet not allow the primary CC holder a guest (speaking to this part "Southwest lounges with unlimited complimentary access for the primary cardmember with complimentary food and drinks, wifi, and power outlets")
That said in lounges if they are really interested in it I kinda think they should look at airports that don't have a big presence in lounges and are also SWA dominant heavy ones to really get an idea of the interest on that since it would be available to a subset of passengers before they just start having lounges all over. The lounge game is crowded and SWA doesn't have the more upscale experience yet.