I don't see the problem. Jack is/was responsible for his own dreams and career. I think Mark inviting him to play with DS opened up many chances and possibilities. Still, it sounds like he just waited until something happened out of the blue by just being at some place (which rarely happens), thinking people were waiting in line to work with him, instead of proactively seeking and chasing opportunities. Mark was already ten steps ahead and moved on. He never wants to live somebody else's dream. With a bit of people skills, Jack should have known Mark was never going to spend a lot of time helping or even starting a new guitar-centric band with him.
And then one other thing. If you're the only member in DS having enough time to see things in the audience that the others don't see, you are way too busy with being a rockstar. Sure they were huge then, but playing MK's music requires an tremendous focus. For MK it's all about the music, and I think he saw very early on Jack had other interests.
