The universe is believed to have consistent laws of physics and there are no contradictions in these laws either.
Is it because the probability of the subatomic particles in the hamburger rearranging themselves and transforming into ice cream is impossible?
A better way to put it, it's because there is nothing that naturally makes the hamburger rearrange itself into ice cream.
All the objects in the universe has properties or attributes, such as mass, weight, speed, temperature, etc. And they have interactions and reactions such as gravity, magnetism, etc.
Consider that an object at motion stays in motion and an object at rest stays at rest until acted upon by an outside force. In our universe, it gets more complicated, but typically there is a cause for every effect and an action behind every reaction. So things do not just transform spontaneously without a reason. The particular example is a very complicated transformation.
I could argue, what if it does transform into ice cream and then immediately transforms back into a burger before you even notice? This is all just speculation, but when you observe nature you'll realize that nature obeys laws and is consistent. Gravity affects us today, and it will tomorrow too, etc.
The only thing scarier than an unexplainable universe is an explainable universe. It seems like there is a rhyme and reason for everything and everything can be understood if we study it hard enough, and that's the scariest part.
Ultimately I think you are asking the opposite question. You are asking "why doesn't it transform," but the real question is "why should it?" The universe works on a "why should it" basis. Nothing happens unless there is a cause and a reason for it to happen.