Del Rio has been unhappy in the WWE for a while now. He only signed a contract with WWE in the first place that guaranteed him certain main event privileges. He sees no benefit in being one of those wrestlers who hover around the mid-card, making a good living and wrestling on television every week. He considers himself amongst the best of the best. In his mind, why shouldn't he? He was a well-respected wrestler before WWE signed him, and when they did finally sign him he excelled. He was given opportunities and he took them. It's only when he stopped being given these opportunities and had to forge some for himself that his work wilted. It was a feedback loop. Del Rio was unhappy at not getting the main event level push he felt he deserved, so he stopped giving his all. WWE noticed this, so saw no reason to re-start his push. Del Rio gets increasingly frustrated; WWE sees less reason to find interesting things for him to do. And so, when a situation arose that meant Del Rio could be fired, and ties severed immediately, the WWE were happy to take it. This is the 9th reason why this works out fine for WWE, but maybe it will work out for Alberto Del Rio too, as...
Michael Palmer is a contributor at whatculture.com and thelineofbestfit.com, and he probably likes WWE slightly more than most people would call "healthy".