Well in the UK, it's usually because the media stir it up. I've experienced several industrial disputes in my lifetime, and on each occasion it was due to failure to agree over deteriorating conditions of employment.

Very often pay deals involve the trading of 'conditions of service' against a pay increase.

Sometimes the employees simply aren't prepared to give up certain conditions, and so they vote to reject the offer.

What then happens is the that the muck-raking journalists see an opportunity to describe a rejected offer as greedy workers wanting more money, when in fact more often they're not happy with the deal.

What's heartbreaking is that everyone usually believes the cr*p they see it on TV or read the papers.