Have you ever left a pint on the counter? It turns into a puddle of sadness. That’s because ice cream is a colloid—a fancy word for a mix that doesn’t settle.
The water molecules freeze, but the fat and sugar interrupt them. That’s why you get small, fine crystals.
If the temperature fluctuates in your freezer? Big, nasty ice crystals form. Your ice cream gets gritty. Sad trombone.