It's because of the MJO IMHO.....if you notice, it always finds a way to minimize both residence and amplitude in phase 8...and even the few days it spends there, it's some non-comital BS like split-forcing. The fast flow is what it is, but it's not fast enough to prevent bombs for the Great Lakes and Canadian Maritimes. I do think CC plays a role, but it's more about the disproportionate warming in the West Pacific predisposing the convective forcing to MC positioning, while repelling it from the more favorable (relative to east coast cyclogenesis) dateline and African continent.