because people who want "eating low meat diets" and "walk, bike, or take public transport" go extinct first.
I’m not the original commenter, but I assume that the reference is that this/your group fairly reliably across most cultures does not maintain the 2.1 children per woman birth rate / replacement rate needed to sustain a population.
At a minimum, this seems to be true for this particular socioeconomic class in most parts of Europe, East Asia, and US/Canada. Not sure about South Asia.