(I do know, though, that I saw two fantastic teachers in my graduate department get denied tenure while I was there because (as we all gathered) their stellar research records might possibly have been even better if they'd spent less time on teaching.)
While most ads you see on TV are about increasing sales, some ads are more about being innovative and catching the attention of other industry insiders to win an award.
I see university research like that. The research part is about increasing the prestige of the university. If they can attract a big name like Dan Ariely with an offer to fund research (and teach one class per term), they can attract press, students, and prestige within their industry.
Another way to look at it is you get lots of prestige by leading the field, and you lead the field by teaching people at conference presentations. Admittedly the people being taught are fellow academics not freshmen, but still...
Finally you could survive in a tenured job with no motivation to be leaders, but given the overproduction of PHDs ranges from merely 10x to as much as 1000x as many as necessary in some liberal arts, the odds of a slacker being hired when only the top 1% can get a tenure track prof job are extremely low, so there is that selection bias against slackers indicating very few profs will be slackers.
Also keep in mind that teaching and classroom management is a skill, one which is rarely taught to young professors. I had a stark realization during my second year of grad school, when we were interviewing a faculty candidate coming straight from grad school: he was interviewing for a professor position, and he did not have significantly more teaching experience than I did.
Now of course this is not for all universities but I think it applies to almost any R1 university, top teaching college, etc. Its not competition for their job that drives them, its just competition against their self-image, competition against peers for prestige, etc.
Additionally, "tenured"/"non-tenured" is not a single binary switch in terms of prestige. Even with tenure there's things to be striving for.