Why aren't Desmond Child and/or Billy Falcon made official members of the band? Desmond Child in particular, just about every song they write together becomes a hit. Why not bring them on officially and collaborate more frequently?

Instead they have Hugh and another guitarist in the band, who aren't credited as members. Seems odd to me. It's not like Desmond and Billy are just song writers, they're both musicians in their own right, and Desmond has a great voice.

I know it's a weird question, but it's something that bugs me from time to time.