Why don’t guys remove you off of social media after they ghost you?

Because we don't care or forget. Girls are the ones who value social media as much as real life. Guys are more reality based in that sense.
They ghosted because they did not care enough to break things off formally. Not bothering to remove someone from social media is an extension of the not caring. It simply isn't worth the effort.
Opinion
4Opinion
It's slightly more work, easier to just not. And they might not think about it.
It's easier to forget/get over a girl when you don't have to see her face every time you come online to talk to someone
Remove them yourself if you want
So they can hit you up later
Forgot or to lazy to bother?
Superb Opinion