It seems that anyone with a piece of land can just create a new development regardless of the the surroundings.
Oh that's sad you think like that. In Thailand it's not like that at all and especially in Phuket. There is a very strict property deed hierarchy, and only the top most deed (called "Chanote") can be built on for residential or commercial purposes. In fact most of Phuket is mountainous and you cannot even build a small hut. Those people that have Chanote land can of course sell it on to investors who would like to develop the area for residential purposes - like my friend that owns this plot.