[hjnilsson]

Because unions need lawyers (and other professionals) to litigate on their behalf. The Venn diagram between lawyers and iron workers/developers/journalists etc. is very slim. So money is required to hire this skill set.

However workers who represent the union are often unpaid. Or paid very little for their efforts.

[mixmastamyk]

Litigation can happen without unions, there was a class-action on overtime pay at one company I worked at that had a payout.

Could a kickstarter or contingency support more cases?

[patmcc]

There was a very recent Supreme Court decision that impacts this - employers can insist (as a condition of employment) that employees use arbitration only for these kind of claims. Which makes class action suits impossible, and leads to more and more wage theft - since stealing $1000 from a bunch of employees would be enough to warrant a lawsuit if done collectively, but not if each individual has to go through arbitration.