Why is x2 . y2 not equal to (x-y) (x+y)?

[Atqiya]

why x2 . y2 = (x-y) (x+y) and xy . y2 cannot be (x-y) (y+y)

 

[kuruman]

why x2 . y2 = (x-y) (x+y) and xy . y2 cannot be (x-y) (y+y)

If by x2 . y2 you mean $x^2\cdot y^2$, then it is not equal to $(x-y)(x+y)$.
It is true that $x^2-y^2=(x-y)(x+y)$. It is also true that $xy-y^2=(\sqrt{xy}-y)(\sqrt{xy}+y)$ . Try substituting $x=8$ and $y=2$ to see how it works.