Please feel free to go deep, e.g. we're living in a neoliberal social imaginary in which the logics of late capitalism constitute a dictatorship of no (perceived) alternatives, and most, unconsciously if not consciously, believe alongside Fukuyama that with the end of the Cold War and the triumph of capitalism as the basis of all human structure and organisation, we have reached the end of history (in which case the public, in general, sees little use anymore for the study of history).
Access to resources.
Academic research is locked behind database paywalls by publishers who do not allow people to buy individual access accounts. It is possible to be a "friend of the library" at most university libraries and acquire book checkout purposes, but database publishers specifically prohibit unis from being able to allow their non-student/faculty members remote (off-campus) access. So if you don't have easily, quick access to a uni library, you're screwed. Because--have you checked out the book prices of your average academic publisher recently?
There are various in-group, experience, and preference factors as well--popular history is very milhist oriented, which both reflects and shapes people's interests; academic history pretty much ghettoizes milhist--but all of those only come into play once someone has access in the first place.