Many factors can play a role such as orientation of the beach, hours of direct sunlight, etc
But most importantly would be the composition of the sand, i.e. what the sand is made up of like rock or shell versus silt etc
Typically the sand that is made up from shell is larger and has more surface area to release heat
The sand in negril is like that and therefore is not typically very hot
However I live in Clearwater where the sand is so fine it actually feels like you are walking in flour....but VERY VERY HOT flour