That’s generally optimizing for cost over speed, empty sites are cheap and going slow tends to save money. It also lets the company constantly move people through a backlog of projects at different locations rather than adding a few people then having breaks in work where you have to let people go.

There is also real physical limitations when moving dirt around. If you quickly make a big pile it settle quite a bit. So instead you add a few inches at a time and bring out heavy equipment then let it settle, do some tests, and repeat.

https://youtu.be/22W5tRWbUVI