A big part of this is probably caused by the fact that the income that you would get at less expensive countries, if you were living, would be much less than in an expensive country, due to the isolation of the labour force from international markets.
If you can somehow obtain an online job that pays in bitcoin, which is a borderless currency that doesn't have country restrictions, you could really take advantage theoretically by going to a country where the cost of living is lower. Practically how this works out is debatable, but it's just an idea.
Actually there are already those who rely on earning bitcoin because it has helped them a lot. Many of the users in this forum participate in signature campaigns so that they may earn bitcoin and this has helped them pay for their daily expenses. It’s not so reliable but it has provided them with some financial assistance. Since the standard income in some countries is not enough to cover for daily expenses due to the high cost of living, there is the need for others to look for sideline jobs like earning btc.