I am a design strategist at a relational design firm whose practice is grounded in cultural anthropology.
We also find it curious how the scope of UX research is so narrow. The issue likely originates with those who hire UX researchers and designers, as leadership (and investors) value quantitative data more than qualitative data.
My colleague, an anthropologist, wrote an article questioning the limits of UX research. https://aegisbrand.com/expanding-qualitative-research-beyond.php