I didn't know folk in the 60's (being a little boy) and resented it violently in the 70s. We (i.e. me and my mates then) saw American influence as pervasive and corrosive. Cultural imperialism, layering on the bougeois imperialism that had marginalised "real" English folk music. The search for "real folk" quickly brought us into contact with the Irish session scene, which was so much more vibrant than anything else we found around (Manchester UK) that I didn't bother with much else for the best part of 20 years.(We'd forgotten about the "English" bit by then).

So I never heard of many excellent folk singers from over there, until much later on. But I'll still reiterate my criticisms from back then, My take on US folk music in 1973 was:

Style trumps content.
It was fashion music- the singers didn't really mean it.
Its roots were shallow (the old are often insanely jealous of the young...)
It had a cachet thanks to media exposure that native traditions didn't have. East altantic traditions had always to be explained, showcased, even apologised for. American music could be played without explanation.
And worst of all, practically ALL the newly composed music based itself on American models. (Actually the stuff that sounded English we thought was of ancient composition...)

So that's one reason why many logstanding UK folkies might not be as familiar with certain artists as they ought to be.