Why is Siri disabled in the new Apple TV (4th Gen) outside US?

I have the new Apple TV (4th Gen). It does have the Siri remote (even though it is advertised as Apple TV Remote here in Singapore). However, when I log in to Singapore Apple ID account, Siri is not available.

After researching, Siri on the new Apple TV currently only available in 8 countries:

• Australia
• Canada
• France
• Germany
• Japan
• Spain
• United Kingdom
• United States

source: https://forums.developer.apple.com/thread/16994

In order to activate Siri, I have to log in using US Apple ID account.

My burning question: iPhones and iPads already support Siri in Singapore. Why does Apple disable Siri in countries which already supports Siri?