#2 Retirement
Shane has always been someone who didn't want to be stuck in his father's shadow, and we can respect that. As opposed to sticking with the company and working under his dad's creation like Stephanie did, Shane felt like he needed to go out and make a name for himself as a businessman on his own. As you can tell, he was pretty successful in the end.
Perhaps, now that he's conquered the business world and had a few more matches, he's ready to ride off into the sunset and spend all of his time with his family. It's not like he's got anything left to prove, and he's probably got more money than he could spend in ten lifetimes. He could quietly slip away or he could give a big retirement speech on SmackDown Live, but either way, it's certainly a possibility.