Specifically because it's meta, even though it's where a lot of people consume media? How else is the government supposed to inform people that don't watch TV or listen to radio?
Honestly, I'd bet that the overlap of FB's current demographics and people who listen to radio/TV is pretty high.
The gov't of Canada has ad spends on bus stops, billboards, cinemas, newspapers, Spotify... I've even seen them on mobile games. If I was Pablo, I wouldn't be very much concerned about the reach of Gov't of Canada ads.
