There were probably a number of factors that led them to there. First of all, they have to be close to a somewhere they can buy more supplies - food, toiletries, diesel/gas, etc. They can't just build in the middle of the sea, they've got to be near somewhere where they can easily land a small boat within easy reach of a supermarket. Climate would also have played a big part in selecting a location. They need somewhere with few storms or hurricanes. They need somewhere where the sea is usually relatively calm and waves are generally small. It would also have depended on various local prices of materials and labor to construct these steadings.