Also, because software developers are like soldiers or litigation lawyers. The more other people have, the more you will need. If company X is your competitor

Also, because software developers are like soldiers or litigation lawyers. The more other people have, the more you will need. If company X is your competitor, and they employ 10 software developers, sooner or later, whatever it is they're working on will release, and that might provide X with a massive competitive advantage over you. So you have to hire your own people to keep up with your side of the arms race. And sometimes, a brand new person comes along with a bunch of software folks to create company Y, and they devastate both you and X within their first 5 years.