Why is concentrated sulfuric acid used for fisher esterification and not dilute sulfuric acid?
Concentrated sulfuric is used to give the maximum yield of product,
The Fischer esterification is an acid-catalyzed equilibrium reaction.
You need the acid to catalyze the reaction and make it run at a reasonable speed.
But, to get the maximum yield, you must remove the water as it is formed (remember Le Châtelier's Principle?).
You are defeating your own purpose if you add water by using dilute sulfuric acid!