It sounds like you were working in one of the industries where the employer was in a consolidated market, so they could absorb the cost of the union without becoming uncompetitive.
That can in theory benefit the union workers, but it comes at the expense of the company's customers, which at scale are ultimately the workers again.
It's also generally not a stable equilibrium, because monopolies are bad and everybody hates them. At some point the government gets around to smacking them with the righteous hammer of antitrust, or the Japanese start making decent cars and disrupt the US auto conglomerates, the internet comes around and destroys your broadcast radio payola system, and then it all turns to rust.
> Businesses have shown time and time again that they're willing to pay as little for as much labour as possible.
Well yes of course. That's what they're supposed to do, so they can charge lower prices and get more customers.
And then what you're supposed to do as an employee is to take the job you like the most based on working conditions and compensation etc. So a company can offer you $25,000/year for 60 hour weeks and no benefits, but if some other company is offering $35,000/year for 60 hour weeks and no benefits then you take that, until the first company starts offering 40 hour weeks and paid sick leave.
A company's ability to underpay people is limited by the willingness of somebody to work for that amount of money. No is a powerful word.
This is also why you get rid of the need for so much of this with a UBI. Because it allows people say no, which requires employers to make better offers.