You're benefitting from an accurate mental model of this code (since you wrote it and work on it) and as soon as someone else has to work on this thing they are going to curse you.
So it might be job security but it's also vulnerable to the hit-by-a-bus problem
When I started out, I wanted to opensource it, it had an installer and everything.. but then I realized it's become kind of a little monster and wisely canceled that plan, I'm not that irresponsible or mean :)
So it might be job security but it's also vulnerable to the hit-by-a-bus problem