The unconfirmed quote in my head: "I think the 'speed limit' changed"
Historically Apple has provided security updates for the current-and-previous-two macOS versions.
For example, Safari 12 says "macOS Sierra 10.12.6, macOS High Sierra 10.13.6, and macOS Mojave 10.14".
They have been doing this since "19 Sept 2012", in when Mountain Lion received its first update. (OS X Mountain Lion v10.8.2, OS X Lion v10.7.5 and Security Update 2012-004)
Where is the Security Update for macOS?!
Updated -> Oct 30, 2018
|macOS Mojave 10.14.1, Security Update 2018-002 High Sierra, Security Update 2018-005 Sierra||macOS Sierra 10.12.6, macOS High Sierra 10.13.6, macOS Mojave 10.14||30 Oct 2018|
Here's the current top of page (Sept 27, 2018)
Name and information link
|macOS Mojave 10.14||MacBook (Early 2015 and later), MacBook Air (Mid 2012 and later), MacBook Pro (Mid 2012 and later), Mac mini (Late 2012 and later), iMac (Late 2012 and later), iMac Pro (all models), Mac Pro (Late 2013, Mid 2010, and Mid 2012 models with recommended Metal-capable graphics processor, including MSI Gaming Radeon RX 560 and Sapphire Radeon PULSE RX 580)||24 Sep 2018|
Looking back a bit, it seems that High Sierra had the same delay. That is only partially comforting to me, I don't see why they can't just declare this as the policy or release strategy.
El Capitan users expected to be dropped with Mojave, but there are a lot of Sierra and High Sierra users that are left wondering if Safari 12 (alone) is enough to keep them current and safe.