It's likely that their long term vision will entail a fully-automated production line (similar to Amazon's logistics goals). In fact it's necessary to churn out units fast enough to hit their production goals. Their recent acquisitions in the factory automation (Grohmann Engineering, etc) will ultimately help alleviate these workers complaints, but perhaps at the expense of their jobs...

That said, there's no excuse for treating employees poorly, even if they're "temporary"...whether it's Tesla, Apple, or Amazon.