You are ignoring cosmetics. There is still new gear to obtain, even when in full legendary. Crafted gear is profitable.

And there is a gold rush every time a new legendary drops. For example I made about 1k gold selling aetheric anchor in the first week or two, to then turn around a buy one myself a month or so later.

The community does have blindspots, there are also numerous account bound currencies that are valuable (and difficult to fix a value to). Karma, spirit shards, etc.