Usually mission statements are crafted to align incentives between employees and customers (or users, if the product you sell to customers is users' attention). The company's mission should focus on what the customer is trying to achieve with the company's product. As the company works toward that mission, customers accomplish their goals, they become dependent upon the product, they fork over lots of money, and the company's revenues rise naturally.

Where this fails is when a company actually achieves its mission. At that point, its original mission is taken for granted, but all of the negative consequences of that mission are suddenly on everyone's mind.

For example, Microsoft's original mission was "A computer on every desk, all running Microsoft software." Throughout the 80s and early 90s, that meant making MS-DOS and Windows easier to use, making Office handle more of the tasks needed for a modern office, and getting distribution deals so that all of these came pre-loaded. Customers benefitted from the increasing computerization, they forked over lots of money, Bill Gates became the richest man on earth. But after around 1998, Microsoft basically succeeded in that, people already had a computer on their desk running Microsoft software, and the biggest problem on their minds was that Microsoft had a stranglehold on PC software and was unfairly killing off new innovations in software.

Google's initial mission statement was "Organize the world's information and make it universally accessible and useful." When search sucked, email sucked, online maps weren't a thing, finding a book meant going to a library, finding an academic paper meant forking over hundreds to Elsevier, and "web browser" meant IE6, this was a huge service to humanity. But then around 2010, they succeeded at all of these, the baseline became "I can find anything I want now", and the huge questions were what kind of information does Google have on us and what sort of nefarious purposes could they use it for?

Facebook's mission was "Make the world a more open and connected place." The world is now a more open and connected place. The result is that people are routinely put in contact with folks whose views they find abhorrent, and that you can influence an election from the other side of the world, and that Facebook has all our personal data. While the world was still cut off from each other, everyone was happy to sign up; now that we're all on one big social network, they're miserable.

Once the mission statement is no longer a problem that needs solving, then the bullshit starts. Without an actual reason for the company to exist or for anyone to do the work they're ostensibly doing, people fall back on "Well, might as well make as much money as we can."