You're looking at it the wrong way. His cake is playing to his base, while helping his investments. Pulling out of the Paris accord does both. The people who care about the climate are not the ones who voted for him.
I mean, S&P 500 index funds are down about a dollar on this news. I'd bet that any minor gain to his investments was wiped out by whatever general market exposure he has, so overall (probably) not a move for him financially.
So he can look like he's getting something done. Almost everything Trump campaigned on was a pipe dream or he has managed to quickly derail if it was even remotely possible. So he needs something to parade around in front of his base even if it's entirely symbolic.
For another example, look at the weird attempted rebrand of existing border fencing as "bollard walls" a while back because the border wall he campaigned on is never going to happen.
You're suggesting that having his cake and eating it too should mean [1] remaining unbound by onerous treaties(because the Paris deal is not very binding and [2] winning the favour of other nations in the deal as well as voters at home who support the deal.
But there is a different cake that he likes to have and eat better: [1] remaining unbound by onerous treaties through the act of withdrawing from them altogether [2] appealing to his base at home by refusing to acknowledge GHG emissions as a problem as well as by appearing to stand up for america by declining to engage in any sort of compromise with other nations.
So he won't withdraw because of any teeth that the deal has.
If he withdraws it will be to keep up the appearance of sharing the same values and beliefs as his constituency.
