He probably watched on TV and figured the training was comparable to training for the Olympics, but as Kurt Angle has said previously the training for WWE/professional wrestling is much harder because there's much more to learn before you even get to the wrestling. There'd been reports for a long while that they wanted him to put more effort into training with them but he wanted to juggle both and ultimately I guess they've decided he either wasn't committed enough to them or improving enough to continue their investment in him. And honestly, nothing of value is lost because his brother in NXT is much better.