SE, it's gotten better, but you are still destroying the game for crafters!

[Jojoya]

I can't understand why people don't understand the value of what they sell for a few hundred gil.

A lot of players never level crafting so they don't have access to desynthesis. Selling the item on the MB ends up being the better way to make gil from it (assuming it will still sell for more than the sell to vendor price).

There are also a lot of people who just don't understand the value of money in general, frequently because other members of their household handle budget.