The problem is that Apple doesn't open-source their drivers and firmware, so those things won't get security updates even if you're using a third-party OS that

The problem is that Apple doesn't open-source their drivers and firmware, so those things won't get security updates even if you're using a third-party OS that otherwise does. If I were in charge, companies would be obligated to keep providing security updates for all hardware they sold until they either did open-source everything, or provided full refunds to everyone who ever bought one.