1 - Crazy road trafic and town pollution (those damn diesel buses exhausting black smoke are terrible). That and the "let's park in the middle of the road because it's illegal to park on the pavement / sidewalk - when there is one).
2 - Bad infrastructure (crappy roads, water & power cuts, shabby internet)
3 - Everything takes forever to do if you don't live in town because of the traffic - and you probably don't want to live in town - so everytime you need some admin done kiss your day goodbye.
4 -Politics isn't based on ideology but on ethnicity / religion which is a drag.
5 - Radicalist and reactionary society, where things like homosexuality still illegal.
Disclaimer : for these 5 reasons I can give 50 reasons why I love Mauritius, including but not limited to my beautiful wife and children, comfortable and relaxed lifestyle, leisure and sport activities. Not every country is perfect, and Mauritius is no exception to the rule.