Narcissism is one likely piece of the answer. Strong narcissists say what they want to believe to be true, regardless of what the facts in the world are, and certainly regardless of what they said last week or last year.

On this particular issue, it’s possible that Elon is trying to be cute. He might have heard something like, you can’t recycle your way out of climate change, and he probably realized that’s true. Plus, he’s heard stories about where things that you put out for recycling actually end up being incinerated or buried in landfills anyway. So he wants to use that as an excuse to attack environmentalists, because as a tech bro he hates environmentalists… Of course that’s just one possible explanation, but even if Elon isn’t using that explanation, other people similar to him surely have and will at different times.