Closed source is not open source, but some software is neither, because open source also implies the freedom to redistribute. Thus, one can sell software with access to the source and freedom to modify it but not to redistribute it. This does not fit either definition strictly.
Most companies who sell their software for money make it closed source so people cannot easily change it or copy it for free.
Even some who give their software for free do not show the source code, because they think it looks bad, or that somebody will change the authors' names to their own (a kind of plagiarism) without making the program better. Some programs called “freeware” are given away for free, but they are not the same as free software that anyone can do whatever they want with.