1.By not employing local population they were preventing social unrest's resultant consequences in the functioning of their own businesses enterprises and hence they prevented political vulnerabilities of employing local populace.
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2.By heavily employing Indian expatriates and welcoming Indian students, they are instilling the sense of secessionism in Indian minds via these people by signaling them (subconsciously) and their nation is not a single entity but several entities formed forcefully and hence they need to break-up.We should not forget that UAE was formed in 1971 when Pakistan was divided to form new nation of Bangladesh and hence western elite created UAE for the very purpose of weakening India by creating UAE.
3.If they would have employed local population in large proportion then the consumption market would not have developed in such a great scale as it has developed now.
4.American troops have to be stationed in UAE as well as in many surrounding states and therefore to cover up the presence of Americans (otherwise people would have been reminded of the days of British colonial times of 19th century) and hence to hide their political colonial presence it was indeed necessary to invite people from other nationalities to diversify the availability of people for western interests.
5.And last but not the least, western elite wanted to experiment that how in a small nation like UAE people of different nationalities can live and that too under the heavy political supremacy of western elite and hence Dubai and Abu Dhabi are satellite cities of European civilizational expansion(just like USA was once open a time when even USA was not USA of now).In fact, it is Israel in proper Arab deserts, now even UAE and Israel have formal friendship agreements."