I don't even know why I have to explain this, but Lovecraft's works != "Lovecraftian". Yes, he wrote poems, letters, philosophical works, scientific writings etc. as well. And yes, there are other prevalent themes as well, such as racism(!).
the fuck is this I don't even
Nobody's talking about his letters, poems, philosophical works, or scientific writings. We're talking about the core of his published fiction.
A lot of it just doesn't fit your simplistic idea of it being only or even mainly about fear of the unknown or unknowable. If Call of Cthulhu, At the Mountains of Madness, The Case of Charles Dexter Ward, and Shadow over Innsmouth don't qualify as Lovecraftian then you have a
very peculiar definition for it.
If I had to condense "Lovecraftian" into a simple definition, I would say it's about the horrific realisation that humans and humanity are not at the centre of the Universe or indeed
in any way important at all. That compared to beings that have come before us, will come after us, and still exist everywhere around us in the greater Cosmos we are utterly insignificant; that none of those godlike powers or incredibly advanced beings give the tiniest shit about us, except perhaps to the extent an entomologist gives a shit about a bug under his microscope. So Lovecraftian cosmic horror isn't about the unknowable, it's about how tiny, puny, short-lived and stupid we are.
This was pretty radical in a context where Christianity with its idea of Man as the living image of God and the crown of Creation was still the dominant mode of thought, much less so now as even Christians will have been exposed to modes of thought that don't put humans at the centre of everything.