Why does aluminum most often have an oxidation state of + 3

Aluminium most often has an oxidation state of + 3 because it has three valence electrons that are removed relatively easily.

Al is in Group 13, so it has three valence electrons.

To get a complete octet, it must either lose three electrons or gain five.

It is easier to remove three electrons, so Al most often has an oxidation state in its compounds.