Dogs snore for the same reasons that humans snore. A partial closing of the throat, or blockage in the nose and throat that cause your dog to make a comical snoring sound.
An adorable little crossbreed puppy laying down in its bed
If your dog is a brachycephalic breed (a dog with a squashed face) it is very likely they will snore due to the shape of their face. These breeds can suffer from collapsed nostrils, an elongated soft palate, or eversion of the laryngeal saccules. All of which can lead to snoring.