OK, so, a monopoly on social media. But so what? You don't HAVE to use social media. It's not like having a monopoly on energy, banking or telecommunications, for example, where you can really put people over a barrel.
You don't HAVE to use energy, banking or telecommunications either. It's not like having a monopoly on food or water. The line you drew here is completely arbitary.
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.
This site gives FB 88.11% currently. Interesting that its trending down slightly:
http://gs.statcounter.com/social-media-stats/all/myanmar