Nothing strange - just think of it from today's perspective. Yes, we do have the advantage of thinking in retrospective
Perhaps it made sense for Samsung to design an APS-C mount a decade ago. But now, Pentax has (DSLR) FF; Sony has (mirrorless) FF; Canon has (mirrorless) FF; Nikon has (mirrorless) FF; Leica/Panasonic/Sigma have (mirrorless) FF. And Samsung wasn't a success story in any case.
In retrospective, Canon's decision to make the EOS-M was a mistake - as they needed to launch another (incompatible with the EOS-M) mirrorless mount; Sony's mount is barely FF capable.
Yes, there's the option of intentionally limit themselves into the APS-C-only corner. Hint: you can use a FF-capable mount for APS-C cameras.
The only advantage would be the theoretical ability to make a somewhat smaller cameras or lenses... but then, just compare higher-end Olympus and Fuji with - say - an A7RIII...
Besides:
a. there's no incentive for Pentax to "save" the failed Samsung NX mount. None whatsoever. Zero. Nada. Nil. So why pay Samsung for it?
b. years ago a Pentax official hypothetically described in an interview a mirrorless mount which would have to be large diameter.
c. Pentax' strategy is at this time DSLR centric.