You "can" make them yourself, but you need to have much more than an email and a phone number. First you need a real IP so that the account doesn't get randomly banned because you used a proxy shared by a ton of people and you started adding friends from sketchy countries(and trust me you won't get quality friends with a fake account) Then the account needs to be active everyday for at least 2 months (posting, adding friends, talking with friends, joining groups)
And then you're guaranteed a ~30% chance it'll actually work and won't get the banned the very second you put in your card, or once you run your ads. And then it'll likely get banned once you start spending over $20 per day on ads.
That's why most people would rather buy, sure you "could" make them yourself, but in the end it most likely won't be worth it.