Why do American Alligators like water so much?
well for one it's their natural habitat. they've evolved for millions of years in it, and it's their habitat niche. in other words they survive best in water either because of food availability, lesser competition with other organisms, temperature or other environmental variables and components of the habitat such as hiding places, and breeding grounds.
not to mention their speed in water is about 10mph versus their not so quick speed on land. which means they are much more able to catch food under water than they are on land. same as we are with land, they are with water.
...because they thrive in it.
These types of questions don't have good answers, sorry.