I hear this often from people in and out of game. I can’t understand how they can think that crafting something was free since they gathered the mats.
Once you have the mats, you have 2 options:
1. Craft them into something.
2. Sell them.
In both cases, you are without the mats in the end, but gain:
1. The value of the item you crafted.
2. The gold gained from selling mats.
So when crafting, the cost was either #2 (gold you would have gotten selling the mats), or the cost of buying the mats, both of which are pretty similar.
And the time it takes to gather should also be taken into account. Time saved can be used to make gold somewhere else.