Because I find it hard to imagine somebody "unfamiliar with school-level math" picking it up in the first place.
I never even made it to pre-calc and I suck at Algebra but I'm teaching myself CS and functional programming. The title made me interested and the warning tells me I'm probably not ready for it.
To me, it seems that the "is not suitable" phrase was a bit condescending. Re-word that, and the warning may be fine.