I think that AC had to move to T1 and T2 and 'give up' T3 in order to better facilitate the switch-over to T-New in a couple of years. It would hardly be reasonable to expect KL, BA, AF, CX etc. and a host of non *A US airlines to move out of T3 to T1 for just a few years and then move back in as soon as AC had vacated it for the new terminal. The charter airlines just ended up moving to T3 (where they were eventually going anyway) by default. If AC wanted the new terminal, they were going to have to endure T1 for a few years.