One could view this as a by-product of the research university vs the teaching university. A research university is supposed to be a place where experts at the

One could view this as a by-product of the research university vs the teaching university. A research university is supposed to be a place where experts at the bleeding-edge of their fields congregate. That expertise is expected to trickle down to their undergraduate teaching, and so the argument goes that only they are qualified enough to prepare those courses. I think this is all largely unwritten and largely unsaid, but undergraduates would be pretty unimpressed if they were getting standardized lectures. A teaching university isn't bound by that sort of expectation, so one could imagine that courses can be more homogenous without penalty. Lots of textbooks provide "sample" slides to use, and if you're teaching out the textbook anyway, you may as well use the slides you're given. Having had no experience at a teaching university, I can't make any claim as to whether this happens with any regularity.