It's not strictly anti-piracy, though the roots are in it. Consumers aren't the only source of requirements. It goes back to content protection deals Disney has cut for years and the reciprocity requirements.

Sounds like you really are not their target market. The primary money making target for Disney is people who watch it on their smart tv. Even if the average joe does decide to fire up their mac they won’t care if it’s not 4K.

Then why do they advertise 4K as an important feature?

Because if they didn't Average Bob would feel like they're missing out.

Some people don't care about 4K. Other people think they care about 4K but don't really know the difference.

"4K streaming" is such a joke

They compress and screw up the video quality so much that even calling it 1080p is a stretch in my opinion

Most people have houses/screens too small for 4K to be visible anyway, though, so I guess it's easy to get away with providing such a crappy service