It wouldn't be a big stretch to say that 90% of quantitative hedge funds use Numpy in some fashion, whether its directly, or via a library that sits on top of it like pandas or tensorflow.
I can't think of a more ubiquitous library in the financial space, maybe QuicFix (http://www.quickfixengine.org/)...
Maybe numpy's problem is visibility?
Possibly it does its job so well that people don't know they are using it when they use library libraries like scikit learn and Pandas?