In the year 2016, a disturbing amount of human activity is run through Excel instead of proper databases.
A similar study from 2009 tested for errors in various operational spreadsheets and concluded, "Our results confirm the general belief among those who have studied spreadsheets that errors are commonplace." The Financial Times commented on the prevalence of spreadsheet errors in business, saying it's probably a function of training and organizational culture.
I've heard from a few salespeople in the software industry that their biggest competitor in the SMB space isn't $BigCRMCorp, but Excel spreadsheets that have acreted over the years.
This absolutely doesn't surprise me. The concept of thinking about where one's data lives is nearly extinct outside of technical circles, and even Access is seen as "too complicated" by a lot of people. The utility of third normal form is obvious to us, but lots of people are perfectly served with pivot tables. How many people receive formal training in any form of database anymore? Even lots of web designers who use MySQL on the back end of their CMS software don't do a whole lot in PHPMyAdmin unless they have to.
Excel is very simple, ubiquitous, and has a low ceiling of functionality. It's the lowest common denominator, and unfortunately, it's "good enough" for lots of people.