I am no fan of unions, but I think they were necessary to force business owners to treat workers decently - to make them pay better than starvation wages, and have decent working conditions. Then came the Cold War, and business owners had an extra incentive to treat workers decently: it undercut communist propaganda, and business owners did not want communism in the country where they owned a business. And so workers didn't think unions were necessary, because they were getting a decent enough deal.

Then the Cold War ended. And about the same time, union membership went into a steep decline. And the business owners have been slurping up all the money in the economy, and paying workers closer and closer to starvation wages. (And there's the working conditions at Amazon, which are... not treating employees decently.) This sounds more and more like the conditions where unions grew strong, because the workers found them to be necessary.