There's a legal obligation to extract the most value for your shareholders. This doesn't apply in sole proprietorships or partnerships with a more centralized ownership, where there's the realistic potential to have a conversation with one of the others (or internally) and say things like "let's do y, because doing x would be fucked, even if it made me more money."

In a publicly traded company, you can literally be sued by your shareholders for not putting profits first. This puts a background pressure that slants the odds in favor of enshitification. And whole industries are based on utilizing slightly uneven odds, so that has a real impact.

As you said - without being publicly traded, people can still be evil, but they aren't nearly as likely.