They have to improve their products continuously to be competitive in the marketplace. Apple's competitive advantage is fundamentally in their software, not their hardware.
They innovate in the hardware space and physical design space, but all of their competitors will make copies of their hardware advantages after a few years. To keep on being competitive, their entire experience has to be superior. And what is harder to copy properly is the software experience.
Engineering cost wise, it's cheaper to just keep the software train rolling than to have older versions persisting that you have to continuously support. That is why they don't charge for it, because it's cheaper for them if you upgrade sooner and become part of the marginal few they can ignore if your a straggler. And 'free' has far higher adoption rates than even $1.00.
They innovate in the hardware space and physical design space, but all of their competitors will make copies of their hardware advantages after a few years. To keep on being competitive, their entire experience has to be superior. And what is harder to copy properly is the software experience.
Engineering cost wise, it's cheaper to just keep the software train rolling than to have older versions persisting that you have to continuously support. That is why they don't charge for it, because it's cheaper for them if you upgrade sooner and become part of the marginal few they can ignore if your a straggler. And 'free' has far higher adoption rates than even $1.00.