Because it's necessary for the plant to function and the government has never seen fit to provide a different arrangement for the work to happen and tacitly approved it as a way for this sort of short-term work to happen. They have quotas to meet, these workers helped them fit the quota, so who cares what effects it has.

It probably requires a lot of work and effort to lay it out explicitly, so they don't. It would be better for workers to figure it out, but that's not the administration's style either.

Hopefully the plant doesn't have to shutdown because of this.