Liquidity. You might not be happy about other people "turning it into cash," but that doesn't necessarily mean you or your investors don't need cash.
Public companies are trying to box out specific areas where they might legally do that: C-corps, mission-based exemptions during public sale, etc
But—and this is full on opinion now—I suspect when the chips are down, the courts will rule that Google can't just burn a pile of value because "we like Science" or somesuch thing. They'll get away with it as long as the pile of money is growing. And hopefully that's "forever". But maybe forever isn't as long as we think it is. The world is changing. Snapchat cometh.
That's when stockholders file lawsuits alleging violation of director fiduciary responsibility. This can happen with a startup if the management proposes a funding round that's a significant lose for existing shareholders. The directors have the obligation to act in the best interest of the stockholders, not the management.
It also comes up when a company has assets and is losing money, and the stockholders want to liquidate and get some money out, while management wants to burn all the cash out to the bitter end.
1. Well they used to be for when society recognized that once a large societal and social phenomenon that is a large corporation (really just lots of people agreeing to work together to do something), that at some point that abstract group had some kind of obligation to the public, given, at some point, it becomes hard to separate the public from the corporations (given who staffs 95% of the roles at such mega-corps).
So basically, public markets were for allowing the public to invest in what had essentially become public phenomenon.
Also, once a company becomes public, it's fucking naive to call it "enjoyable" and assume that's as nuanced as you get when thinking about that decision.
Also, you're an idiot. "A company going public wants to take on some debt."
No, they want to sell equity, specifically because they would rather do that than sell bonds ie raise debt.
Public markets seem to be for people who want to take on some debt or are tired of being responsible for the future of their business.