I think the root cause is one layer of abstraction away from the stock market: the federal reserve. It's federal reserve policy, primarily interest rates, that drive these boom and bust cycles. The stock market/companies are just riding the wave.

Sure, the last few years are an extreme example. But I don't believe it's just the Fed, there are other factors at play.

I've only been old/educated enough to follow it since around 2000, and there's been a direct correlation between fed policy and the markets. After 9/11 they dropped rates which created the housing bubble, then when they tried to raise interest rates the housing bubble popped in 2008, so they lowered rates again. We've been at near 0 percent interest for years, creating the current bubble/inflation. They are now putting downward pressure on the money supply which is causing the banks to crash, housing is not far behind, etc.

This isn't to suggest there's no other factors, but monetary policy is a major driving force in the boom/bust cycle.

Unionization didn't really help in the heavily unionized rust belt when the jobs went overseas.

offshoring labor is the companies' answer to unionization.

Why would a company entertain demands of Spoiled Tech Dudes Union, whose work can be performed by people overseas equipped with ChatGPT for a fraction of cost?

This could be not too distant the future, if IT workers decide to unionize

Unions can improve pay and conditions, they can't really do anything about market forces.

Here in the UK the unions are medium-strong and haven't prevented self checkouts, ticket sellers being replaced with machines, etc.

What you need is strong labor laws. A universal three or six month notice period in favour of the employee would do wonders to prevent overhiring and overfiring.