Not every Netflix Original is available in every region. This can be either because Netflix was producing the show before they were in that region, and so signed over the rights to the show in that region to a different provider, or because they have agreements with other producers that need to be on board as well. The same idiosyncrasies will probably apply to downloads.

For instance, in the case of Luke Cage, maybe Marvel needs to sign off on delivery changes like this? Hard to determine without looking at Netflix's actual contracts.

I would imagine agreements regarding distribution rights. Netflix (distributor) can only offline stuff they have the rights to.

HK in particular I would assume Netflix (content producer) are interested in partnering with a Chinese company as that region tends to favour those quite heavily.

They said it wasn't going to be available for every title yet.