Gasha boxes are the #1 hot seller in f2p games usually. In our game whenever we put a new pet or costume piece we would sell literal thousands of those things. People would spend like $300-500 easily in a weekend on the gashas.
GW2 uses almost exactly the same model we used in our cash shop. We even had a gem/gold exchange.
I am sure the Black Lion Chests/Keys [we also had a chest/key scheme too!] bring in gobs of money for Anet.
The cash shop is very savvy.