Here's why:
* Petit is the French word for "small" and is used as an adjective to describe the size of the cut of meat.
* Filet is the French word for "fillet" and refers to a tender cut of meat.
Therefore, petit filet is the accurate way to describe a small, tender cut of meat.
While "petite" can refer to something small, it's generally used to describe things that are dainty or delicate, and not necessarily a cut of meat.