At most major universities in the United States, the advice that junior faculty get from their senior colleagues about the optimal division of effort between research and teaching usually boils down to something like the following: Research is paramount! Put enough effort into your teaching so that (1) students aren’t complaining to the Department Chair and (2) students say they don’t hate the course on the course evaluations, and you’ll be fine.
The truth is that this often directly reflects the weightings given these activities during evaluations for promotion and tenure. What keeps research institutions running are research dollars coming into the institution, and what keeps research dollars flowing in is the research productivity of the faculty. Thus, research productivity becomes paramount, and the incentive structure is constructed to make it so. Consequently, this causes most faculty (and administrators) to see research and teaching as a zero-sum game.