Why not? To put this into perspective, Facebook was founded in 2004. This is relatively recent. Internet and World Wide Web existed fine without advertisement sponsored gardens of Facebook since around 1990. There is no reason why there necessarily should be Facebook in the Internet landscape.

It's not impossible to imagine that, say, Microsoft and Apple, in competition for users, could start filtering advertisements in the browsers. That this pulls users from Chrome. And changes the landscape yet another time.