Very often they do. Many of these internal applications are from mainframe computer times when interacting with applications exclusively via the keyboard shortcuts was the norm. In most companies, they never dared to remove those because the Power Users are used to them for decades.

Problem is, few people are trained directly by those power users so they never learn those efficient shortcuts. And they are never well documented.

The trend definitely comes from the fact that new people get overwhelmed by cluttered user interfaces. But just having a clean initial screen doesn't mean good UX. Good UX is the art of providing a clean, logical user interface that's simple and efficient to use. Unfortunately, too many companies just go for minimalism and wind up with things both taking longer and ending up being harder to use.