I think the primary issue here is that there isnt a universal plug solution. It is all dependent on your wiring setup. What if you don't want a tone knob? what if you want 2 volumes? what if you want a kill switch
? what if you want to coil split? what if you want to wire it out of phase? How do you know what your switch should do. To remedy this, they would have to use one plug per wire. Anyone who has wired up an hsh will know that there are dozens of wires. this would require a whole mess of connections, eating up valuable cavity space. I know I like neat cable management. This would only cost a few dollars per guitar, but more than likely would just create more complication than help. I think it would be useful to wire yourself a connector if you know your setup and are just changing pickups
often. Also, this would theoretically create more issues, since now you have a solder joint AND a plug connection.