What makes you think the social media landscape of almost any country in the world isn't dominated by US-based services? They only need to provide a localized version to get into a market, which they then end up dominating through international network effects.

The only country I'm aware of where domestic services are dominant is China, and the statcounter data does reflect that. They are conspicuously missing WeChat and QQ, though (which are messaging applications and probably hard to track for a third party), so maybe there's some local service in Myanmar that similarly falls through the cracks.