Workers got complacent because they didn't understand what the union actually did for them and they listened to the business propaganda. Unions don't appear out of thin air. They are formed because a business is screwing its employees to a breaking point.
If you're in a union job, it's a guarantee that same job in the past had a fraction of the pay and benefits you have now and previous workers stopped putting up with it.
Not just union jobs, but traditionally union industries like auto workers as well. I have a friend that works in a factory in the US south. Not union, but the pay and benefits are close to keep UAW from gaining a foothold. He would complain about them handing out flyers in front of the plant every so often.
After a recent incident that had him sweating bullets over potentially losing his job for something minor (and having to face management and HR alone), I told him to take the leaflet next time. I hope he does.