The only reason I've heard that isn't super handwavy is that measuring it would require a wavelength with enough energy to create a black hole. IDK if that's true or not, and IDK if that also means the distance doesn't exist or if it's just not measurable.

I've also heard that there's nothing special about planck length other than it being universal constant that we and any conceivable aliens would agree on as a standard of measure. So, idk.