My company still has machines we made in 1950 that customers use in their business. They buy replacement parts from us. While we would love if each of those customers spent half a million dollars every few years to replace those old machines, we can't force them to do that. We can make some money from replacement parts though, so long as we are willing to set out sights low enough. Things that old are mostly mechanical so it is easy for someone to learn how to support them, and it saves the customers a lot of money. In the end we are proud that things we made 70 years ago are still being used in the real world for their original purpose.

You should learn the same: take pride in the fact that things you wrote years ago are still useful. Part of that means write good code so that it is easy to fix any newly discovered hack, without having to update everything else to the latest.