It's the person who doesn't know how to do that yet. Most people don't get started in software development by writing their own operating system kernel. They're using an existing application with published source code and want to make a little change. It's an ugly hack written by a teenager, they just want to use it for themselves. They'll get better at it as they do it more.

But now you say they have to buy a Mac and pay $100/year. Well, that's a no for that little initial change, so now they never get started to begin with.