The idea that you can have an economically sound career talking about historical colonialism is a bit far-fetched. There are a few authors who probably scrape by a living writing books on this topic, but that's about it (and they don't need a degree to do this). If you get one of the handful of academic jobs where you teach this topic to other students, it is something of a racket, where you are teaching students to get a degree in a field where the only job is teaching other students this topic. There is certainly inherent value in some fields that don't have a direct application, like philosophy, but can still inform other pursuits.

As for the politicization of the field of colonialism studies, generally, these sort of topics are viewed through a pseudo-religious lens today, the religion being utopianism, the idea that there can be survival and satisfaction for all. Under the utopianist worldview, practical concerns are ignored and the topic is judged under a lens of morality and dogma. That makes it an unserious field and marred by activism. Very true for many humanities and social graduate degrees. Might as well go to seminary and spend half a decade learning to be a theologian. The outcome is similar, dogmatic and removed from reality, makes it hard to transfer into a real world setting.