Well, number one, why would they? Apple makes money by getting consumers and locking them into their unicorns and rainbows ecosystem where everything is perfect which makes consumers comfortable spending boat loads of money, not by selling commodity hardware.

Ecosystems with great UX and paid subscriptions plus a 30% cut on all transactions are far more profitable than the margins you make selling commodity hardware. Just ask famous phone manufacturers like Siemens, Nokia and Blackberry why that is. That's why SW dev salaries are much higher than HW dev salaries as the former generates way more revenue than the latter. That's why Apple doesn't roll out their own cloud datacenters and instead just gets Amazon, Microsoft and Google to compete against each other on pricing.

Apple only rolls out their solutions when they have an impact on the final UX, like designing their own M1 silicon.

And number two, selling chips comes with a lot of hassle like providing support to your partners like Intel and AMD do. Pretty sure they don't want to bother with that.

Before they start selling chips I would rather they open iMessage to other platforms to eliminate the bubble color discrimination.