You can, but not easily.

It's 2019, it is easy these days. With GNU/Linux, DuckDuckGo, Mastodon, Matrix, XMPP, microG, F-Droid etc. it's just a matter of giving it a try. The hard thing isn't staying away from the big four - it's untangling yourself from all the network effects you already got yourself into.

That's why it's not easy. Most people are already entangled in those networks. They use Google Docs to write papers and presentations, they have an Android phone, a GMail address, and the websites they visit are filled with trackers for all sorts of things. It's entirely possible to avoid all of these things, but not easy. It requires a certain amount of technological savvy that most people don't have. It should be within easy reach of everybody, and it's really not.