Partly, it's for personal publicity. However, I think he continues to champion this fake cause because his ego was so irrevocably damaged by losing the Presidency. He needs to throw himself headfirst into some cause he can champion in order not to give into despair.
Think about it. He went from being practically President of the United States of America to a punch line in a joke in a matter of a couple months. He gained at least 50 pounds as a result of this battering of his damaged psyche.
He needs to feel important, so he's created this cause that (very cleverly) can never end because he's changed the name to "climate change", which encompasses absolutely everything. Hence, he can never be proven wrong by labeling something as climate change.
Yeah, Gore is a huge hyprocrite, but a good businessman. Remember, he owns the company to which you and I are supposed to buy those carbon credits. So, if you hear he personally bought carbon credits... big deal ! It's like he's paying himself.
By the way, don't let these GW fanatics try to convince you that GW is real. Every new study that comes out now more fully debunks the theory. If you watch the following video, you'll realize it's all one massive hoax.