Because it’s cheaper for people to do it.
Here’s what i mean.
It would take time to develop systems that run the automation for that job. That development cost is probably more than paying a person minimum wage to do the job.
Besides, people are more flexible too. You can just walk over to them and tell them to change how they’re doing that job and they do it! If they don’t fire them and hire a replacement for the same minimum wage.
Elon Musk said one reason why the Tesla factories are not totally automated was because it took a person to take a hose that is flailing around and connect it to the right place. Not so easy for a machine to do!