Why is $\mathbb{Z}_{100}$ bad for cryptography and how can it exploited.

Question

I read that fields like $\mathbb{Z}_{p}$ given $p$ is prime ensures that the key is "equally distributed". This makes it hard to reverse engineer and find any exploitable properties. I want to know what these properties are. For example, how can one deduce or find any additional information if the field was $\mathbb{Z}_{100}$. I know the basics of Finite Fields and why they're needed in cryptography. I need a simple explanation why $\mathbb{Z}_{100}$ isn't desirable.