This is largely due to differences in the history of different disciplines, as well as differences in the types of knowledge that is valued and how these values appear in writing. In more STEM-oriented fields, it is not common to explicitly state the theories underlying the research, but they definitely exist, regardless of whether the author acknowledges them. For example, the "scientific method" itself is a Western theoretical framework that has origins in the history of empiricism, positivism, and objectivity (all of which are also Western theoretical frameworks underlying much research in the "hard" sciences). These frameworks are not explicitly mentioned in research papers mostly due to tradition - they are simply assumed for certain fields. Many researchers in the sciences would not necessarily even think of these things as theoretical frameworks because the way that researchers are trained in those disciplines (usually) does not include debate about different theories or foundational assumptions. If you are interested in learning more about this, I'd suggest looking into the history and philosophy of science. A good starting point would be the work of Thomas Kuhn, e.g. his book The Structure of Scientific Revolutions. Regardless, it's important to note that the theoretical frameworks currently active and popular in the sciences are mostly all Western inventions, and there is a decent amount of Western chauvinism involved in the assumption of these frameworks around the world.