ok, the reason why ppsc is default to my understanding, is because they dont want noobs going cd the moment they think they're going to lose. the current system encourages players to fight for every last supply centre they can get their hands on. it also allows other players to 'buy in' to existing games as someone previously cd and improve their number of supply centres to gain points.
the problem with wta is that although it does encourage people to "play to win" and not just get as many centres as possible at the end of the game, it offers no incentives to stay in the game when they are getting smashed. More experienced players may have a "code of honour" to never quit.
in short, its to try and stop civil disorder. how effective it is, i dont know. but 1 problem i see is that most noobies only have 100

, therefore no incentive to cling onto that last sc.