Depends on the type of person buying the gold.
Someone who's got the end game gear like you said - probably buying it for PvM supplies/final game upgrades (Tbow/Scythe/Inquisitor)
Someone who's got a gambling addiction - as staking is best in game gold, but can also be worst

Someone who's flipping gold, typically from BnP - trying to cash out with their FG
Someone who doesn't have their account maxed and wants to get 99 buyables.
Lots of things influence it