Guild Wars 2

Why can we trade the latter on the TP, but not the former (all ascended weapon parts are account bound AFAIK)?

I wondered this myself but it doesnt make any difference in the end, as the base ingredients (asc ingots, planks, squares) for weapon parts are tradeable.

To eliminate money bags from simply buying a set. Same reason as some of the components are time gated. You want it, vertical progression, make it yourself.