Reasons for orbital inclinations I see that there was already about Pluto's orbital inclination, but I would like to ask a more general question.

Why do planets have orbital inclinations?  And is there any particular reason, other than chance, for Mercury's inclination being so small?

Thank you!
The planets formed from a disc of dust and gas. Since the orbiting the proto-sun formed into a disc the planets, which formed from this matter are in a disc too, but not a perfect disc. There was some scattering of the matter in the primordial disc, and so the planets are also slightly scattered. Interactions between the planets have also scattered the planets out from the disc too. The formation of the planets caused them to have small, but not exactly zero inclination

The Earth has the greatest inclination (except pluto) however, by convention, we measure inclination relative to the Earth, all the planets have a positive inclination.

So there is no special reason that the planets have slight inclinations. It is just what would be expected due to random effects during their formation.