With all the employees back in the office, they’ll have plenty of time to hang around the water cooler and discuss all the ways to unionize. Leaving the company is great as an individual, it sends a message. Unionizing helps to restore the balance of power vs rights and is exactly what Amazon doesn’t want. This (IMHO) is how you “F them hard”. Additionally, it’d send a message to the other companies who want to flex on the people who make the company work.