My understanding is that crunch time (as well as the release of flagrantly buggy games with patches coming later) is driven primarily by marketing schedules/budgets. Ad buys, press releases, interviews etc. are negotiated and coordinated months in advance, and big releases from any given publisher need to be staggered largely so that they don't all demand marketing money at the same time.

Publishers give advances, have milestones, etc. It is uncertain whether a game will make money out in the market, but part of a publisher's role is supposed to be to have a portfolio and be able to spread that risk, funding some of the development of both the losers and the winners.