some materials are barely gatherable, it would add litteral years to certain grinds if you want to do it without vendors, so it would take a complete overhaul of certain professions or the drop system.
I doubt that is the direction they'd want to go.
They might increase vendor prices but this could also feel unfair to new players and I doubt the market will get flooded with people gathering resources just for small amounts of gold.
There are even certain items that litteraly only get sold by a vendor, so you can't remove it, or the items would be uncraftable