A new employee is like a newborn
They need nurturing and confidence building and they proceed with baby steps in their new job. There is always a cost at having a new employee, even for the simplest job. There will be an overlap of work with an experienced employee so that the new employee can get to know their way around, know what to do and how to do it. The more specialized the work is, the longer the training takes.
You can also expect a new employee to produce low quality products or services at the beginning. This will also add to your cost of a new employee.