How about these reasons that matter to a manufacturer: Skylake CPUs cost about as much as their Broadwell predecessors, and there is very minimal motherboard redesign required (sunk costs are low). Nearly all competitors have moved to Skylake, and are flaunting it's improvements that make the current rMB look bad in comparison; where thought leaders in the consumer electronics media have noticed this, and are recommending buyers away from the rMB (opportunity costs are high). In sum, the cost to update is low, but the cost of not updating is higher. In these terms, there is nearly no reason for Apple not to release a Skylake update.
Finally the argument that Apple has bigger fish to fry is irrelevant. They're a big company, they have the manpower to dedicate to it all. Especially when it comes to simple hardware updates such as this.
The issue I have with this theory is that with the RMB barely in stock in all colors/sizes in all stores for 6 months it makes no sense for Apple to take the markdowns on existing inventory, liquidate existing inventory, and replace all the samples in all the stores all for the sake of an update that I think we both agree won't move the sales needle at all. Besides hardcore types like the handful in this subforum, who exactly waltzes in to an Apple store asking about processors and milliseconds of betterment? No one.
It's just too soon, that's all. And no matter the size of the company, each product has a P&L and the RMB hasn't even begun to pay for itself, all the R&D, all the inventory, it just isn't good business sense to transition so quickly on a machine that honestly doesn't need it yet from a performance standpoint or a sales standpoint.
Now, if Apple were to address all the negative press, that's a whole other can of worms, they'd be adding USB-A ports, they'd be adding an HD camera, they'd go back to a Chicklet keyboard, in other words they'd just discontinue the thing. We all know what drives these bad reviews, right? Money. Make a pro-RMB video on YouTube, no clicks. Slam the thing as an affront to God, ton's of clicks, thousands of ad dollars.
But we both know what's going to happen here- Apple is going to thin down the Pro and Air, they're going to put in retina displays and USB-C ports and plateaued batteries and all the rest and as a result make all these frustrated Pro and Air owners happy with something new and that will put an end to these silly complaints about the RMB. In the end, the whiners don't want an RMB. They want a thin Air with a retina display. When they get it, they'll stop the nonsense.
BJ