why does my corn snake stay on the cool end of the tank alllll the time

First of all, kudos for providing your snake with a warm and a cool side of the tank.

Corn snakes, in the wild, like to have temperatures that are between 79 and 85 degrees Fahrenheit with nighttime temperatures falling to around 70 degrees Fahrenheit.

Make sure to have thermometers on both the cool and warm side of the tank so that you may be able to analyze and regulate the temperature on both sides.

If you use a heating mat under the tank, make sure to check the temperature of that as well and to make sure there is enough bedding so that the snake doesn't get too warm, as heated glass can get VERY hot.

If you have a thermometer and it's reading too high, try a lower wattage bulb. Ask the person at the pet store, who is experienced with reptiles, what wattage can give the temperature range that your snake needs.

Also, make sure that you have hide boxes on both sides of the tank. If your snake only has one hide box on the cool end, chances are high that it will prefer to hide rather than to be warm.

To whomever said that snakes need UV light, don't listen to them. Snakes are one of the only reptiles that do NOT need UV in order to survive. Here's why: UV lamps provide UVA and UVB rays that reptiles get from basking in natural sunlight and it helps to build healthy bones by providing the important Vitamin D to their bloodstream. The reptiles that mainly need these UV lamps are reptiles that strictly rely on a vegetarian diet (iguanas and some turtles, for example). Snakes, on the other hand, being carnivorous, get all of the Vitamin D that they need from the animals that they eat. So a UV lamp isn't necessary but it won't hurt the animal if you decide to use one.