Because software is all about scale. The larger you are, the more profitable you are. If we sell twice as much as software, it doesn't cost us twice as much to build that software. So the more customers you have, the more scale you have. The larger you are, the more profitable you are.
If you're putting your name on something, it's really important to be a part of it, or else people will just do whatever they want with it. And then it's not really you, and it won't be true.