To extend on what /u/doomladen said, the Falklands has a maritime tundra climate similar to that of Iceland or the Alaskan Panhandle. In other words, while it doesn't get particularly cold in winter in comparison to most of Northern Europe, it barely has any kind of summer at all - the average summer maximum is only around 13C. It is virtually treeless and extremely windswept, and has very poor soil, making it not terribly suitable for most types of agriculture other than sheep grazing. Hence why it wouldn't have been terribly attractive to a settler in the 19th Century.

One obvious point is climate - Mauritius is far more hospitable, with readily available food sources year-round that easily permit a larger, stable population and encourages migration there.