Apple is fighting too many competitors at the moment. It used to just be Microsoft, but Google's dominance in smartphones and slow but constant pressure in tablets and "good enough for most people" laptops is causing the company to lose focus.
Microsoft also traditionally didn't have a credible hardware story, giving Apple a complete vertical integration story. Now both major competitors are vertically integrating (Microsoft with Windows + Surface and Google with Android/ChromeOS + Pixel).
I think Apple is having to choose where they're going to focus and tbh, the Mac line is a smaller line of business for the company. If you simply don't use a laptop/desktop at all, then nobody cares that you can't connect your other devices cleanly to it, your other devices are your primary computing devices.
Microsoft doesn't have a good story on the phone front, but it's not inconceivable that they'll try again with a shrunk down surface line if the it proves successful enough.
Google's desktop story is also incomplete, but they're moving rapidly towards something if they ever stop having OS confusion.
The iPad Pro is large and powerful enough that it basically can be the "good enough for most people" computing device. And they have a cohesive ecosystem from small to large in the iDevices.
There's no significant future for Apple with the Mac line and the company is allergic to commodification in ways that their competitors aren't (and that's where that line is heading). Apple is more likely to keep playing with iDevice sizing and software than to continue dedicated serious resources to keeping the Mac line alive.
I'm not calling it a deathwatch yet, but it's clear it's a backburner line of business for the company.