Not necessarily and by that I do not judge about open source. Often when people want to describe open source and how it is created. It seems the developer program all the fancy stuff from the goodness of there heart and if they don’t they don’t even share there stuff not from the goodness of there heart. The most software that I am using today is open source and most of it was developed and shared because of try and hard business-interests. And do I think that is good? Yes, of course. And there are a bunch of reasons why people create openSource software.
When you build a company internal tool, it will probably only get developed as far as necessary to fulfill the current needs. Even it the tool would have a much greater potential. In your company it will left behind, it will do its job and as soon as you need some additional functionality someone has to analyse the code and implement it. When you publish it as open source. The company can later be lucky. Maybe someone else needed that new functionality together with that tool too. So he implemented it and you just need to pull the changes. That will have saved money and time in both of your pockets.
Not just that, when a company is going to open source some code. The company what that tool to have a good image and transport that image back to the company. So before publishing code in the name of the company, they will take some actions to improve the quality. In that process, it is very likely that they not just improve the quality of the existing functionality but also add some close related functionality that is easy to implement and valuable to the project.
In business, the most expensive thing is time. When the developer you are going to hire need a week or two to learn your tools, the company actually pay that guy or girl to study. For the company it would be more interesting to hire someone who already knows how to work with the own software. That is motivating the company also to improve the documentation. write it down once, many next developer can learn and that is a great deal for anyone.
And here you got it, with the hard facts of business, you see, how great software is getting developed as open source, even in companies that just think for there own advantage.