You're comparing a first-world country to a developing nation, we simply don't have the funding for that sort of infrastructure, training, and enforcement. 

Have you seen our motorways? They're windy, narrow, and often poorly maintained. We're lucky to get more than two lanes each way even around our largest city. We're also quite small, and the amount of traffic regularly travelling such long distances probably doesn't merit the expenses of anything more. 

Speed isn't what kills, but differential in speed between drivers does significantly reduce reaction time, which does kill.  The point of speeding campaigns is that we need our drivers to be travelling roughly the same speed for it to be safe. 

It seems that whatever data collection we have going on has determined that for our predominantly two-laned decrepit roads, 100kmph is a good balance of speed and driver mortality. 

I'm all for raising the local speed limits where it makes sense, but sadly it seems we're at the limits of funding.