It's been hard as hell for anyone to be a proper wrestling heel in the modern era.
Sweeping statement, sure, but an accurate one. Heat-seeking has never been more difficult, because wrestlers play before a switched-on audience who (for the most part) no longer willingly boo like sheep when promoters say so. There has to be a reason for the hate, a reason for fans to jeer and a satisfying argument for why crowds should bay for blood.
One of the most effective is when those people feel a performer has shot to the top without their approval, like Roman Reigns, or spurned their support.
This is something WWE has been able to use as a tool. Ask yourself this question: why do you dislike the wrestlers you do? What is it about their character or presentation that provokes outbursts of anger or annoyance?
Could it be, in some cases, that you actually once loved and respected them? It's a bit of a funky thought, but what if some wrestlers had/have more potency because they managed to first endear themselves as likeable, even when they weren't strictly faces...