If companies are desperate to retain and hire employees, then management should bend over backwards to make sure employees are happy, including answering "why" to out-of-the-blue deadlines. If a manager is upset at answering "why", then that person is NOT a good manager.
If jobs are hard to come by, then companies can get away with the "my way or the highway" attitude. It won't make for happy employees, and may result in higher turnover. Pick your poison.