My thoughts are McDonalds likes to hire young staff, so its a lot of people’s first jobs. Now that they’ve got work, oh shit I should join the union. But ya, next day likely not, but the union didn’t call a sympathy strike on day 1 either. It was many years later, lots of time to have actual representation at the store. (edit: And it looks like the food workers at McDonalds partook in the strike, so they were members by then)