Annual updates are the problem. You can't do 18+ months of development work in 12 months. You can do 12 months worth, and then 6 months of what is essentially incomplete software as point releases.
It took 8 years to progress through Panther, Tiger, Leopard, Snow Leopard, and Lion. In the next 8 years we had Mountain Lion, Mavericks, Yosemite, El Capitan, Sierra, High Sierra, Mojave and Catalina.
Fifteen years ago we used to mock companies with 12 month release cycles. Now we (and the market) have become addicted to it. Apple has had three pauses to tidy up code - Snow Leopard, Mountain Lion and High Sierra. I predict they will do one more major release before releasing a tidy up version.