What did the builder say the cut outs are for?

I know at least one was for plumbing.

How could they cut access holes before the drywall was installed? Prepare a template, cut the acess holes before installing the drywall?

Why are you so rude? This is a forum. A forum is for asking questions. Get an education.

Do not accuse good advice of being rude.

They could be chasing leaks. They could be allowing inspections they missed. They could be installing access panels. They could be installing low voltage. The question is not dumb, it is just too vague (especially without pictures) to zero in on an acceptable answer.

What Is the Airspeed Velocity of an Unladen Swallow?

African or European?

We'd really need to know a lot more about the age of the particular swallow in question (I understand they fly quite slowly just prior to death) and the environmental conditions (e.g., temperature, windspeed, direction of the bird's flight relative to wind direction, etc.) Assuming standard conditions, 20 mph would be a reasonable engineering approximation.

What are they doing?

Fixing mistakes. Best psychic guess is outlets, switches and/or electrical boxes covered up by drywall crews.

Guys working don't do things for entertainment or just for fun. Something didn't pass inspection. Sounds like they couldn't get air pressure to hold in a water supply line when they did a check. Or a neutral and ground wire got mixed up on a wiring circuit. Drywall is easy to patch. It's probably repaired by now.

The age of the swallow, I don't know that! Auuuuuuuugh!