Meddler or Other Rioters, Fill me in on this questions upon ADC champions

Ashe's ult does AP damage only. Ezreal's ult does AP and AD damage. Lucian's ult does AP and AD damage. Miss Fortune's ult does AP damage. Corki's ult does AP/ADC damage.

I kinda get why Ashe's ult is only AP damage but why is it only AP damage compared to Ezreal's?

also

Why is Miss Fortune's Ult only AP if it's a physical type of skill just like corki's?