C/B teamed up in 2011, pre-split (2012). I don't think they ever publicly said why they chose to go with Igor, but we can probably assume it was the ability to get more attention and be more of a top team/priority, which they wouldn't have been with Marina.As far as politiks are concerned, Spilband must have been hibernating for a long time, because for years after the split it hadn't seemed to help his top-level teams, aside from shopping for spare parts and putting Chock/Bates together, because they left him over time,
IIRC, Igor did work with some top int'l teams during the early years, like Pechalat/Bourzat and Cappellini/Lanotte (although the latter i think was short-term/summer).

