It consists in the fact that the beach umbrellas on the local beaches are close to each other, creating a continuous shade. In such a shade it is very comfortable and safe to relax, without fear of falling asleep and getting a small sunburn 🏖️🙂

Neither in Cyprus, where we lived for 5 years, nor in other countries that we visited, we have not seen such umbrellas. This is some separate feature of Thailand 🙂
The photo was taken on Koh Larn Island.
One of the things Thai beaches are missing is proper facilities to rinse off seawater and sand. A simple outdoor beach shower, commonly found on many beaches in other countries, would be a great addition here—or at least basic foot-washing stations to remove sand.