That’s right, Penn is the only one of the 8 Ivies that is not in that NSF top 50 for STEM PhD production.
Penn also is the lowest-ranked Ivy for overall PhD production.
I don’t disagree that Cal, Michigan, and UVa, have relatively high PhD production,
although even Berkeley’s STEM rate is not as high as 7 of the Ivies or 34 other (non-Ivy) private schools. And yes, any number of factors might contribute to the difference.