Because it fit into an ecosystem of tech that is constantly evolving. Software as a whole evolves more quickly than most tech. You see the same effect in every other branch of engineering but just slower.

Example: They are having problems rebuilding a certain famous church in Europe that burned down because the trees that went into it are now all smaller. They can't get a replacement part.

I just dealt with this about a month ago at work. A customer machine died and they wanted "an exact replacement". I explained to sales that is all I need to hear to know this project is going to be a disaster. Parts go out of stock, the network stuff is not as backwards compatible as people think it is, and standards change. They went over my head and demanded the same machine. I get daily emails from our fabricators about the problems they are having. Engineering is not a once and done thing. You need to have the staff and resources to continue to make your product match up with the environment it is in.