It's as simple as considering revenue shares:
- iPhone (%) 50.65%
- iPad (%) 6.13%
- Mac (%) 8.21%
- Services (%) 26.30%
- Wearables, Home & Accessories (%) 8.72%"
In total, Macs, especially desktop Macs, don't sell in high enough numbers or earn Apple enough to warrant the frequent and big hardware upgrades we see for iPhone and other more mobile devices.
Apple earns far(!) more on its array of fully or semi-incompatible with non-Apple products-products and services, like iPhone, iPad, Watch, AirPods, etc.
Another way to look at it is that Macs sit "outside" Apple's Walle Garden, and don't really incentivize sales of apps through Apple's App Store(s), or purchasing AirPods, Watch, etc.
Lots of freedom for Mac owners when it comes to headphones, hardware accessories and apps means, comparatively, far fewer profits for Apple's shareholders.
Just the hardware price for your average Mac is a "gate" that makes them much less accessible to the masses, leading to lower sales, comparatively. iPhone, iPad, Watch, etc., can be bought on payment plans, with all kinds of deals and trade-in discounts, making them far more attractive and easier to acquire.
It's also the same reason Apple has been so slow at improving AAA gaming on Macs: Revenue generated by App Store mobile games are absolutely phenomenal. Both by comparison to competitors and to Macs. Cheap to make and can earn perpetually.
Consumers naturally aren't playing these games on their Macs but on iPhone and iPad.
Overall, it's just about prioritizing the products and services that that consumers increasingly want that also earn Apple the most, which is mobile devices, iPhone, iPad, Apple Vision Pro, etc.
Although nothing drastic from year to year, I'd expect new Mac releases to slow exponentially over time. Maybe even get retired entirely in 10-20 years depending on how fast products like Apple Vision Pro can be improved.
Are we expecting the kids growing up with AI devices to know how to or need to operate a desktop computer like the Macs we have today?