There are a few good reasons to sue as a share holder. The first is that you just have different interests. For example, the board and CEO decide to do somethin

There are a few good reasons to sue as a share holder. The first is that you just have different interests. For example, the board and CEO decide to do something that benefits themselves and their other financial interests. In that case you can sue and stop them doing whatever it was. So it's a mechanism of control - and you don't need a shareholder vote or a majority of support, what you can force can be unpopular but in your interests. That was the pretext for Tesla getting sued for Elon Musks' compensation package - the shareholder won and Musk had to hand back billions in compensation, that's strictly a financial gain for the shareholders. But secondly, there's the meta game. If you're a good lawyer and you spot some company doing something egregious you can go shopping. Go and find a shareholder and say "Hey, we can sue that company, I'll take care of all of it, I just need your name because you're a shareholder". You can then conduct a massive expensive lawsuit against the company and if you win? They have to pay your exorbitant costs. Going back to the Musk example, the shareholder who sued to reverse the compensation package had a derisory number of shares, but the lawyers who took on that case are now asking for something like $5Bn in costs. That's a pretty nice payday, and in some ways it works like a bounty against companies with poor governance.