Emails from people following you

Ever since I joined I kept getting these emails that someone followed me, which I thought was pretty cool. It gives me a reason to stay on the platform in order to gain a small following.
It wasn't until I found out why exactly I got these emails that I thought it was awesome instead of just cool.

It is because when you visit dev.to the next people to sign on are encouraged to follow the latest active user on their website (in this case me).

Growth hacker marketing

This is one of the tactics that Twitter used to grow their audience, namely letting people follow someone as soon as they sign up to the platform (described in the book growth hacker marketing).
Dev.to probably uses this tactic to make sure new users have something to read and give smaller publishers, like me, the ability to grow.