Why would the shareholders want to risk turning the company into a smoking hole in the ground and making their shares worthless?
That said I think it’s a bit suspicious when so much of the ownership is institutional investors who seem to just own each other, and appear to work against the very interest of maintaining and growing the value of the investment, which is what one would think being a shareholder is all about.
There are plenty of ways to make shareholder value without actually improving Boeing's product safety culture. Even if the planes are deathtraps, what are customers going to do about it? Sue? Lawsuits will take years. Buy Airbus planes? Order queue's backed up for years. Ground their fleets? Then they can't make money. Every solution takes years while shareholders have to worry about the next 90 days. Even those with a long position can just propose that the company start selling off assets in order to make up the losses. That's what corporate raiders do, and it's what happened to GE.
Shareholders do not care about companies. They care about making money.
The original sin is paying executives with stocks and especially stock options. It creates catastrophic and corrupting incentive structure.
Their incentive is to raise the stock price long enough to sell some amount of stock options. The company be damned.
There are many examples, but the classic one is Dick Fuld, the CEO of Lehman Brothers. He drove Lehman Brothers into Bankruptcy all while becoming dynastically rich.
Stock compensation for execs should have much longer timelines. You should have to hold the bag for a minimum of 18+ months after you depart, although 5 years would be better.
The stock market is not a requirement of capitalism. Nor is it a requirement for management to be beholden to shareholders in the short term. It's a culture problem. Apple for example, gives two shits about shareholder short/medium term concerns about sinking billions into the Apple Car and Apple Vision Pro that may take a very very long time to become profitable (if ever.)