The monopoly _does_ exist in AI: machine learning is entirely data driven, and companies like Facebook and Twitter quite literally have investors throwing money at them because they have such valuable data for that purpose. Google is no different.
Data is the commodity. There is nowhere else you can get good raw data about, say, what people were publicly discussing last week, except through Twitter, in order to guess the stock market. Much of that data is closed off or incomplete even through their API. There is no other option except to create another Twitter.