Why does does vegan pulled pork specifically require jackfruit?
It is simply because jackfruit has a consistency and texture that makes it very well suited in a substitute for pulled pork.

Apparently, you can also use hearts of palm, but according to an earlier question, it's harder to acquire and not as good as jackfruit. Here's a mushroom-based recipe. A google search for "vegan pulled pork -jackfruit" renders many more recipes without jackfruit.

In Sweden, where I live, we have pulled pork substitutes made from soy protein available in grocery stores. Perhaps something similar is available to you.