Because Apple has never released a Macbook update in less than 200 days from last update
This is just wrong.
Late 2008 (October 14) and Early 2009 (Jan 6) - 84 days
Early 2009 (March 3) and Mid 2009 (June 8) - 97 days
Late 2012 (October 23) and Early 2013 (February 13) - 113 days
Most notably, these updates were related to updates where they split the updates between the sizes like they did here in 2015 with the 13" in March and the 15" in May.
If they released in October, they'd be over 130 days which isn't even in the running for the shortest release cycle. Furthermore, I think that getting hung up on the days between releases as a barometer of Apple's
intention is ridiculous. Apple doesn't have a counter on their wall that says "we can't release another product for X number of days". The days between releases is directly correlated to when the technology became available. Nothing more. If anything, the Mid-2015 update of the 15" is an outlier which should be ignored anyway if you insist on getting hung up on the "number of days" concept.
The 5257U proc in 13" came out in Q1 2015. The 13" update came out in Q1 2015.
The 4278U proc in the Mid 2014 (July 29) 13" came out in Q3 2014.
The 4258U and 4750HQ in the Late 2013 13" and 15" (Oct 22) came out in Q3 2014.
Clearly, Apple will be releasing the Skylake update within a month of the Skylake procs becoming available. Both their historical release cycle and basic logic would support this. Customers are finicky and Apple can't simply rely on people buying their products because of the logo. They'll keep up with the rest of the pack in that respect, with no concern to the number of days since the last update.... if you can even call the Mid-2015 15" update an update.
Everything really depends on Intel. The speculation should be limited to (a) when will Intel be shipping the Skylake chips, and (b) which of those chips will Apple be selecting for the 13" and 15" models. The current roadmap shows the majority of mobile "H" i7's being released in September and one in Oct-Nov, while only showing two "H" i5's, one each with the September or Oct-Nov release date.
If Intel meets their goals and
if Apple chooses the i5-6300HQ and i7-6820HQ for the 13" and 15" respectfully, we'll probably see an update in September or October depending on how early in the month Intel gets the goods out.