Developed nations are prosperous ones, and have a high standard of living and per capita incomes and also, a much more developed economic/busines system, whereby entrepreneurship and business acumen is rewarded adequately and properly on the basis of innovation and originality.
Thus, quite obviously, 'individualism' is highly valued and rated, in many ways, in such societies/economies. The standard definition states that Individualism is a philosophy, stance, ideology, doctrine, attitude etc, that stresses the 'moral worth of the individual over the mass' i.e. that is, it's the opposite of collectivism, which is the attitude/doctrine/philosophy/ideology etc, which seeks 'safety' in numbers in collective action and activity.
In a developing society/economy, people are afraid of risk/s economic and otherwise, as there is no socio-economic security; whereas in developed nations, societies and economies, risks are taken and decisions made that reflect a greater or higher degree of individualism, rather than sticking to the 'herd mentality' of developing societies. There are a number of detailed studies, some of which are mentioned below, which further this idea, or thesis, better.