It's not concrete, but I always believed apart of the reason why shane left was because he knew his dad was never going to make him heir to the throne. I don't believe there was no serious animosity between the both of them, but I believe she had a part in his departure.
Stephanie gained more ground with Vince than Shane as time move forward.
I know Shane might deny the whole rivalry with steph to save face, but I always felt like shane didn't get the proper respect he wanted so he left and did his own thing.