16% is a decent market share. Apple could lower the premium profit margin of its products, increase its market share, and likely make more money overall by doing so. However, they aren't interested in this.
Also remember that the more common macOS is, the more of a target for malware it becomes.
Apple has been interested in market share for a long time. Apple is no longer just a "premium only" company. iPhone SE, iPad 10.2, Watch SE, Homepod Mini all prove this.
Not only do people who buy entry-level Apple products eventually upgrade to the Pro lineup, but they also get hooked into buying Apple subscriptions too which is Apple's primary growth driver nowadays.
Having a more common OS and being targeted more by malware is a good problem to have.
And put it this way, the more common macOS is, the better software support will be for Pro users because developers will actually optimize for Apple Silicon.
Steve Jobs was interviewed on this many years back, and was accused of selling expensive, overpriced machines. His answer was basically "Well, we actually try to price them very affordably. We don't want to make expensive machines, we just want to make the best machines. And we won't compromise on that just to try to focus solely on price."
Steve Jobs said they didn't know how to make a cheap computer that wasn't junk. They do now. It's called Apple Silicon.
Cheaper MacBooks would just cannibalise the current market. You might get new sales to MacOS virgins but long time Mac users will buy the cheap MacBooks instead of more expensive models.
It will cannibalize it by a little, yes. This is unavoidable. But it should be net overall positive. I would never buy a Macbook SE over a 16" Macbook Pro. But I would buy the Macbook SE as a gift to my family members who don't own a Mac yet but already own an iPhone and an iPad.
Even a $500 MacBook won't substantially change macOS market share. Wintel got in the market first and they own it.
Nah. In the US, the iPhone is now 52% of the phone market but Macs are only around 15%. This means far more people have an iPhone + Windows than iPhone + Mac. People want to buy into the Apple ecosystem but Macs have always been too costly at the entry-level price point. Apple has a big opportunity to sell Macs to existing iPhone users with something like a Macbook SE.
The question is also whether they actually want to increase the market share.
Yes, they do. Apple wants market share now. They clearly show this with affordable iPhones, iPads, Watches, Homepod Mini. Apple's strategy has changed from capturing only the premium market to now capturing the low-mid-end all the way to the highest end.
Produce excellent value products using Apple Silicon, manufacturing scale, and older designs. Capture market share. Get people to subscribe to services. Upsell the low-end customers when they increase their income.
And remember, an iPhone + Mac customer is a far stronger ecosystem hook than just a standalone iPhone customer. Every additional Apple device a customer owns will entrench them into the ecosystem that much more.