Theories as to why Illusion falls under Personality?

I honestly feel it's a bit of a pity skill for an attribute that is otherwise quite situational. Speechcraft can be quickly replaced by Illusion spells, and eventually money once you know how to get tons of it. Mercantile has the same issue IMO

In particular I'm looking for roleplay explanations. Like I think it makes sense for unarmored to be under speed, whereas Illusion has always confused me. I might argue Illusion should go to Willpower, role-playing wise?