This is exactly why spite is a great motivator - it encourages people to do better game theory (in the context of the ancestral evolutionary environment, at least). If you never go after the $25 someone owes you just out of spite, people will repeatedly take advantage of you in ways that aren't worth remedying.
In a more just world, there would be a way for common people to avail the benefits of our legal system without sacrificing a day of work, mailing snail-mail letters and faxing forms in triplicate. If a company owes me $25, why can't I just take them to small claims court with a simple E-mail to my county court?
According to the article around 60,000 people have found the time to make this happen.
What we are seeing is a fundamental aspect of human nature and that is that spite is a great motivator.
You're right, most people can't afford to do this, but many can. Enough that it is hitting Uber where it hurts -- the bottom line.
And as someone who favours stronger protections for workers that is most pleasing.