What makes people collect them?
Collecting them are suppose to increase your odds to get Master Writs from doing crafting dailies.
However: I'm not sure if you need the whole set from each style for it to count or not. Would be helpful if someone more knowledgeable than me could clear that up.
But that's why I collect them. So I can obtain and make Master Writs. Unless of course it's a style I actually use for my outfit. Then I collect them for cosmetic reasons.
Yeah unfortunately it's only completed styles that are counted towards the improved chance of master writs.
The same thing that happens when you catch all the fish for the master angler achievement - nothing.
You do it for the sense of accomplishment and completion, you get nothing more than satisfaction and that is enough for me.
I want the Master Crafter achievement.