Here's why:
* Holes are often individual and distinct. Unlike animals or objects, holes don't usually form a cohesive group.
* The context matters. The type of holes would influence what collective noun might be used. For example, you might talk about a "cluster" of holes in a piece of cloth or a "network" of holes in a honeycomb.
Instead of a specific collective noun, you could use a descriptive phrase like:
* A series of holes
* A network of holes
* A cluster of holes
* A multitude of holes
The best way to describe a group of holes would depend on the specific situation and the desired effect.