Lust, Gluttany, and Envy are just different forms of greed. Why are they treated as distinctly different sins?
I think you answer your own question. Although I don’t necessarily agree with the premise that they are all the same.
Greed to me implies wanting and hoarding, wanting to have and possibly not letting go.
Lust for instance may not necessarily imply never letting go but simply to have, in a sexual way, and maybe only once.
Gluttony is kind of just like renting something because we know you don’t keep it forever.
Envy is more of an emotion you may not actually desire the thing somebody else has you are just emotional about the fact that they have it.
Just my two cents worth.