A tool is needed to not only tie together data from a few different systems, but to add just that little extra functionality that none of the other apps have. It may have even started off as something that a Business Analyst built solely for her purpose but others caught wind so it was released into the wild. It is so well received by the business that they request a few enhancements as well as a little more functionality that would save them big dollars and automate some of their tasks. Before long, the business now has a mission-critical MS Access application that needs to be supported and production-alized by someone (IT?).
Fortunately, and contrary to what many will tell you, there are ways to make an MS Access application stable, and quite useful. As with anything, there is the right and wrong tool for each need, but used in the right context MS Access can be a win-win for the business as well as IT.