GF
Coils are clogged with dust. Clean the coils (usually on bottom or rear). Or the freezer is not getting enough air to the coils. Remove things that are up against the bottom of the freezer so air can defrost the coils.
The coils are too cold because they're dirty and air can't pass through them
Spock (rhp)
ask Whirlpool support page, using exact model number. be prepared to call for what should be free warranty service. you do have to make sure the passages by which air circulates are not blocked with your food. -- grampa
Jimmy C
You might be blocking the vent holes where the air circulates if you have too much food there.
Robsteriark
Totally normal if your freezer is not a “frost-free” model.
If it is a frost-free model then either the air circulation fan in the freezer has failed, or you have loaded the freezer in a way which is preventing air circulation: the user manual should have guidance about that and there are often interior labels advising of areas to keep clear.
Frost-free models also prevent the build-up of frost but few models totally stop it from happening. Once frost starts, almost no models get rid of it, and once started it builds faster.
It is very possible that someone left the door ajar on one or two occasions. That’s all it takes for frost to get started. So if you’re sure it’s loaded correctly and fault-free, remove the freezer contents in freezer bags, defrost the freezer and wipe the interior thoroughly dry, and then replace the contents being careful to remove all frost from them and dry them if possible.