>Another way to look at it is that each other state's Elector selection process is their business.

Similarly, the entire election is the business of every citizen. "Their business" has a direct impact on my life, so I should have some say in the matter.

>The Constitution does not provide any assurances that other states will choose their Electors by any particular process,

The Constitution sets up the electoral college. That doesn't make it a good system.