Supply, meet demand. There are lots of people who want to teach part time for the title and even more who desperately cling to the hope they’ll be able to get a tenure track job after being told they won’t, for many years.
Research output determines rankings. Teaching quality doesn't.
Now, at least some of this is academia having too strong of a filter, but the year I joined Berkeley - I was 1 of 4 to accept the offer.