Look at good guy Exxon sticking up for the planet /s
It's an easy PR win for them, cause the Paris Agreement is more symbolic than anything, as it is woefully ineffective at actually punishing countries for failing to meet targets, so if Trump chooses to stay, they can milk the environmentally friendly PR and the status quo continues. It actually hurts them if Trump chooses to leave cause it puts them into the spotlight.
While it sounds a bit defeatist, he does make a brilliant point. All of this is no good if all the leaders of the worst offenders outright refuse to attend these events and actually commit their countries to meaningful change.