It's not out of spite. Healthcare is a fixed cost for employees. Overtime costs more per hour in pay. Undertime costs more per hour because the same fixed costs

It's not out of spite. Healthcare is a fixed cost for employees. Overtime costs more per hour in pay. Undertime costs more per hour because the same fixed costs are divided over fewer hours. If Uber has to pay fixed costs, they have a greater incentive to minimize undertime.