Ehh customer will get peeved if Apple updated the lineup in less then a year again. Apple probably wants to space to back to a year to look normalize the schedule again. Idk though if they released sooner I’d be happy expect we still haven’t seen new H series proccesors.
Why should they? Even with that obnoxious 527 day gap between the 2015 and 2016 models, the average time between updates is only 303 days. If you take out that wait, the average drops to 258 days, which is only 40 days from now. It's not like Mac updates follow any "normal" schedule like iPhone releases - they (have to) release them whenever the new chips are ready to stay competitive.
Also, pretty much any 13" notebook out there is now quad-core, with Apple being one of very few exceptions. This is not like in previous years, where a new CPU generation got you 5% more performance. We're talking about a 40% or more performance boost here. I cannot imagine Apple likes to be in a position where every competing notebook, even at less than half the price, is so much faster than their own products.