Given the cost of using the court system it simply isn't worth suing for small ammounts of money. Small claims court helps to an extent but for most people it still won't be worth if the value of the damage is less than a few hundred dollars (and if you value your time and are well paid quite possiblly not even then).
Sometimes a company can do a small ammount of damage to a lot of people. If a company with a million customers screws each of them out of $10 then they have dishonestly gained $10 million. That is clearly a sum where it is worth going to the expense of using proper court procedures to consider the case but only if all the damage can be considered at once in one court case. Hence the reason for class actions.
Having said that while I like the principle of class action lawsuits I don't agree with the practice of paying victims damages by using vouchers which will encourage them to go back to the company that screwed them rather than something that can easilly be spent anywhere.