Interestingly a number of these things on this list aren't unfettered good things. E.g reducing iron absorption, or increasing fuel efficiency, e.g if you're vegan, or you're trying to lose weight respectively those aren't good things. So I think that resolves the mystery, it's not a missing nutrient, it's just a chemical that can be used to offset consequences of other patterns of consuming exogenous molecules
Regarding absorbing iron on a plant based diet, it's important to distinguish between heme iron and nonheme iron, and that namely most vegans have no trouble getting enough iron from beans and greens.
