I can understand to some degree why the Friesian School of thought is ignored in Philosophy. It is not exactly Kantian because of significant disagreements with Kant e.g the discursivity thesis. So if one is interested in Kant, he would not think of looking into almost any of the Neo Kantian philosophers. Plus Fries is not exactly constructing a tightly intricately constructed  Gothic Structure like Kant did or Hegel.

It takes generations for the implications of the Fries doctrine of immediate non intuitive knowledge to get put together in any sort of structure that could rival Kant of Hegel.

Still I find that the final synthesis of Dr Kelley Ross to where he pulls together all the threads of the Frisian approach to be quite impressive. See: https://www.friesian.com/foundatn.htm

Mainly because this corresponded with my own experience in which I felt I had faith that was not derived by logic nor by experience.  And this makes sense in terms of the Middle Ages in which Faith and reason were considered two different kinds of sources of knowledge.

And as Hume noted: reason does not tell us any where as much. as it was thought to show.