Variance in academic fecundity during and after graduate school Some people used to be prolific when they were working on their PhDs, but years after graduation, they hardly published a single paper. Why?

Also, some faculty members published great papers while working on their PhDs that received dozens of citations, but few years later and after they started leading their own research, most of their published work barely got any citation. How come?
I'm sure there are more reasons, but here are two positive reasons.

Some people get a job that stresses teaching more than research and so they put their focus there. It can be a rewarding life, actually. Lots of teaching and a bit of research. Maybe less stress. Of course this is an unlikely scenario at an R1 university. 

Some people, after gaining tenure and leading a fairly large group of graduate students in a lab or research group, are willing to let the students gain the glory and don't add themselves as co-author, even though it might be appropriate. This isn't a good path before tenure, but can be afterwards. So they are doing research but, by feeding ideas to them, the students gain the credit for it.