It creates the potential for unexpected support consequences and brand destruction. For example, say I run a sketchy reseller operation that buys old or refurb

It creates the potential for unexpected support consequences and brand destruction. For example, say I run a sketchy reseller operation that buys old or refurbished Apple equipment and load an iOS-ish/macOS-ish custom unix (and then falsely market it as an "Apple product"). For all intents and purposes, it may look exactly like an official Apple OS, but it isn't. The untrained eye is oblivious to the differences and now, assuming the "sell" was that that person got an Apple device for cheap from some random seller, Apple now has the potential burden of supporting that. Considering their potential market is in the millions who might be duped by this, by allowing this one little change, they just introduced a support burden that nukes their profit.