Unfortunately, I can't tell you why, other than to say that I suspect OneCare is released to countries based on licensing, support, and other mysterious factors.
In which countries and languages is Windows Live OneCare available?
The Windows Live OneCare subscription service is available in the following countries and languages: Australia (English), Austria (German), Belgium (Dutch, French), Canada (English, French), France (French), Germany (German), Ireland (English), Italy (Italian), Japan (Japanese), Mexico (Spanish), Netherlands (Dutch), New Zealand (English), Singapore (English), Spain (Spanish), Switzerland (French, German), United Kingdom (English), United States (English, Spanish).
Pasted from <http://onecare.live.com/standard/en-us/faq.htm>
-steve