SilverWook said:

Is it possible a lot of those films didn't get much exposure on television?

I saw most of the Frankenstein, Dracula, and Mummy sequels on tv growing up, but never even heard of the Paula films before.

Give that man a cookie.

After reading your comment, I looked it up. That's it! The original "Shock Theater" syndicated horror film package for television, that guys like Svengoolie and Vampira used to host, did not include a great many of these unloved films.

That avalanched into Forrest Ackerman not loving them, them not being in "Famous Monsters of Filmland" magazine, and not being remade by Hammer.

Imagine an alternate world where David Prowse starred in "The Brute Man" remake, and Peter Cushing turned an ape into Ingrid Pitt.