Apple has never been shy to cannibalize their own sales, in fact it's straight out of the Steve Jobs playbook (“If you don’t cannibalize yourself, someone else will”). I'd challenge you to find a company better at it than they are.
Examples include:
iPod mini cannibalizing iPod
iPhone cannibalizing all iPods
iPad cannibalizing Macs
iPad (2017) cannibalizing iPad Pro
iPhone XR cannibalizing iPhone XS
They're even organized to support product cannibalization, being functionally organized instead of divisionally. If they had an 'iPod division', that division would fight tooth & nail against the 'iPhone division' to keep their P&L running.
They're not doing a 2-in-1 because it's not a product they feel makes sense right now. That's all.