Good question, Hunnie. In simple answer, the internet is a dot com world. Statistically and naturally, people tend to think of dot com as the extension to most websites. Therefore, it has become part of branding & marketing for business owners. Even smartphone keyboard layouts include a visible dot com button first (until you hold down for other extensions).
You brought a great example of FAFSA.gov. Most people would mistakenly visit FAFSA.com because of what stated above & in much greater traffic volume than FAFSA.net. The best solution is to own all top level domains (.com, .net, .info, .org, e.g.) for your business.