It may sound simplistic but its the truth and there are plenty of other examples and history around this - Starbucks recently. 30 employees unionizing may not have any significant impact on their profits, but if they let that union grow it would have a lot more members demanding better working hours or wages over time. A strong union also generally leads to a loss of control by management where they have to negotiate more with workers which they don't like. Why do you think they were fired?

Firings in this case were for union busting. Illegal union busting is profitable - that's why business owners do it. Because it's illegal, they will make up a different excuse for why the workers were fired. They will never admit to illegal union busting. So you should not take their statements as good faith.

Profit = revenue - expenses.

Firings reduce expenses, the equation above explains the rest. Of course, that's only in the short term, but that's what exec bonuses are given out on!