This is true to a large extent by personal and anecdotal experience. As a result, our countrymen''s gifts, their brainpower, skills, tenacity and work ethic are put at the service of a foreign country. Who are left behind are the less competent and less enterprising. No better proof of this can be found in the dismal state of our affairs. (Might not all the politicians decide to leave one day?) The other reason is the development of the countries that absorb migrant labor. The US, being the land of immigrants, is the prime example.
I have a different view of the matter. While I concede the existence of the external conditions that make life so difficult here, that is graft, pollution, politicking, crab mentality, etc., it does not necessarily follow that migration has resulted in a brain drain as passionately argued by nationalists. By this I mean that for every person who leaves, it creates a position or an opportunity for some others. We have enough creative people to fill in the gaps even if working abroad is their main motivation to work hard. There are a constant renewal of human resources development and motivation to inspire people. These do not happen regularly enough in many of our red-tape organizations.