I agree with N0, this isn't a case of GW wants moar moneyz, this is actually the case of good marketing for FFG, hoping to draw in existing marine table top players (of which there are a ton) to their tabletop game. Add to that that if they use chapters with their own codex, they have all the fluff they'll ever need on hand and can either be super lazy and have a day with /copy, /paste for the whole background section of the book, or they can take that time saved and work on the mysterious and hopefully home brewed chapter 6.
as for, what is the appeal of playing the anti-social party member? Who here doesn't like say... Wolverine? or other generic bad boy doesn't go with the flow just to be a pain in the rest of the party's butt character? You all know you have a pc who loves that character type
I think I have... 3 pcs who like doing that... god this is gonna be a pain in the butt lol.