He was funding a Pro-Trump, Anti-Hillary Clinton troll campaign [1], which drew a lot of controversy, as the early Oculus VR audience (developers and technologists) were demographically opposed to that type of ideology.

I think he was fired because he was generating a lot of negative press/attention for what was at that time a burgeoning VR project dependent on adoption by a crowd that largely wasn't a fan of his political leanings...basically office politics.

But...he was fired with a $100 million severance [2], so it's not much of a pity situation.

1 - https://www.theatlantic.com/technology/archive/2016/09/reven...

2- https://www.fastcompany.com/90266150/zuck-pressured-facebook...