I have 14 characters. I am not going to spend 1500 crowns per character unlocking outfit slots. However, if they were account-wide I would probably buy at least 3. Even if they cost more per slot.
I doubt I am the only person who would do this. I know there are people who probably pay the 1500 per character but I suspect that overall account-wide slots would bring in more Crowns.
I have millions of gold, so it's not as though I care about spending 7000 gold to change my outfit. It's more the convenience of not having to choose all the pieces and colors etc..
I have the Crowns too. I just think 1500 crowns per slot per character is a bad deal. It would not be hard to have an additional option, so it's not as though the current method has to go away if there's that one guy who's going to say they prefer it.