They do, but there are good reasons for people to become reliant on social media to fulfill their human need for social connection.
There's a comment from someone who had an accident and was literally stuck at home, I know of a few reddit moderators who were severely handicapped, there's people who moved country or town and don't have their childhood/uni social network anymore, people with mental health issues, people stuck living in the middle of nowhere, the gay kid who lives in a homophobic town, the atheist who lives in a deeply muslim country, etc.
Obviously it's not ideal, but social media are their way to connect. Often they have no real alternative.
It's easy to look down on them, and assume it reflects poorly on them, but often you have very little choice in these things. Shit happens and you end up with few real life friends.
It all happens to us anyway, especially men. Wouldn't be surprised if the majority of middle-aged men have no friends at all.