Some areas have different ingredients depending on what’s available. Here in the United States, real pumpkin is preferred. You can use any gourd to make a pie but for the true pumpkin pie aficionados like myself, I can tell the difference when someone uses real pumpkin vs butternut squash vs sweet potato vs just creme, eggs, and brown sugar and some flour (I’m looking at you, Wegmans).

In the southeast coast of US, if you make a “pumpkin pie” with squash, you won’t be invited back next year.

Given that my mother, grandmother, and I, were born in the States, I can definitely say that "preferred" isn't as wide spread as you think it is.