St Lucia is in a very temperate climate and much of the island is a rainforest, prime conditions for bugs to thrive. We have methods to try to control their population but we can’t eliminate them entirely.
Some mosquitoes in St Lucia can transmit diseases. However, they have to bite someone with the disease and then bite you to give you the disease. This kind of mosquito does not usually fly more than about a quarter of a mile, so being in places of low population density (such as at Villa Grand Piton) lowers the likelihood that a mosquito will bite an infected person and then fly far enough to bite you and transmit the disease. So although it is possible, it is very unlikely.