I often see people asking why so many users are willing to keep shelling out all the money it costs for products like Adobe Acrobat Pro, when free or inexpensive commercial or shareware alternatives are all over the place that would allow you to edit a PDF document and save a modified copy. Same goes for Adobe Photoshop, or even Microsoft Office.
The answer is most cases is that the familiarity makes it worthwhile. I mean, yes, in a minority of cases, you actually have users who need advanced features or functionality that's not provided by any of the alternatives. But I'd say the vast majority of the time, it's simply that someone spent years using those "name brand" products for the work they do, and switching to something else that has menu options in totally different places, and toolbars with different icons for the functions they're after doesn't seem like a good value to them.