The fact that you don't like customisation doesn't mean it is the same way for everybody.. Just check For fashion on reddit and you will see there is a big part of the community who is really into it. (Edit) The guy who said he only use one slot deleted his com.
I completly agree with MiniMiniMaggot, with one years and a half of weekly content there is waaaay too much possiblities for 3 slots. Like the devs want to give us effects, ornaments, gear... but don't want us to use it! Plus, it would have any negative effect to increase the loadouts and make a lot of people happy.