I really don't understand crafting.

[Sagittarian]

I have really dumb question. Why do it? Like just kind of want to know why the big goal is here.

What's the goal in playing the game in general? Not trying to be snarky - this is a question that has a different answer for everyone.
Some people enjoy crafting. Some people find it useful for making gil or equipping their adventuring classes. Some people enjoy being able to help/supply others. Some people want to do everything possible in the game. Some people just want to add stuff to their FC house.