Daniel Eran Dilger of Apple Insider wrote this editorial about the future of the Mac

Editorial: The future of Apple's Macintosh

Thinking about the future of Apple's Macintosh becomes more realistic when grounded in facts. It's no accident that several Mac models have not been updated in many months, but it's also true that Apple faces real constraints in dramatically expanding its Mac sales. Here's a look at what's involved, and what's possible for the future of Apple's graphical mouse-based computing platform. There are two primary factors in the future of the Macintosh: macOS as a software platform, and Mac hardware. Apple has been relentless in updating macOS software. It has issued a dozen major new versions over the past sixteen years, roughly twice as many major new releases as Microsoft's Windows over the same period. Apple's latest macOS 10.12 Sierra release officially supports Mac hardware from 2010. More troubling to many Mac users--and potential Mac buyers with specialized needs--is that fact that some of Apple's Mac hardware hasn't been updated for years, creating uncertainty about whether Apple still values some of its smaller niche businesses that were once considered strategically important, including pro audio, video, graphics and publishing. This is particularly the case in the face of the massive adoption of iOS, Apple's Post-PC platform powering iPhone and iPad, which has become the company's primary source of revenue and profits.

Where're the updates to existing Macs?

Consider Apple's current Compare Mac Models page, which lists a dozen Mac products. Seven of those are notebooks, three are iMacs, and two haven't been materially updated in years: Mac mini and Mac Pro. Last October's Late 2016 MacBook Pro was also considered a delayed refresh; the company's best selling high-end notebooks hadn't been previously updated in more than a year. However, that model got more than just a new speed bump; Read more about that speed bump here.