It is a mystery

Cream is a very specific wet fat; it's hard to fake. The non-dairy, non-soy substitutes are coconut cream (taste issues, doesn't set on its own) and cashew cream (really doesn't set on its own); I'm scared of trying "let's add a lot of tapioca to pumpkin" because I figure the first four tries would approximate pumpkin spice ballistic gelatin.

Kinda like gluten-free bread; you can get something that's enjoyable to eat, but gluten is what makes the sponge and allows leavened bread, it's not really substitutable so you can get actual bread in gluten-free baking. Much the same with how custards or ganache or any of the other milk puddings set.