Willard so much better known

Probably because it's the first. The original is almost always more well known and beloved than the sequels (with rare exceptions like The Devil's Rejects and maybe Dawn of the Dead). And it also got that remake in 2003 so that helps it stay more fresh in people's minds.

But maybe that'll all change when Scream Factory releases their Blu-Rays of both films very soon. It may get the recognition it deserves.