I apologize if this seems overly simplistic, but as I understand it, US law prohibits the sanctioning of strikes under various circumstances, typically because they would be too disruptive to essential services or the economy.
For example, nurses can't strike because patients would die. OK, I can buy this so far.
Teachers can't strike because this would rob parents of taxpayer funded childcare. Seems shaky, but OK.
People can't strike against multiple shipping giants at the same time (across multiple employers in an industry) because this would disrupt the larger economy too much.
So, we don't sanction strikes by the workers whose sheer essentialness should prevent them from ever NEEDING to strike, but who often still live in poverty, and often other forms of danger as well. Those who CAN strike, can strike only against a single employer and not a whole industry.
By design, this makes American strikes (I don't know how much is legal in other countries) seemingly designed not to be very effective, except in a tangle with an individual employer. A large employer will often have the power to fund sophisticated approaches to employing scabs, and could probably easily subcontract a lot of work to a rival not going through a strike, cutting their losses sharply.
In practice, it seems like our labor laws take hard leverage off the table completely, and mostly reduce labor unions to helping individuals inside potentially corrupt organizations, but prevent them from doing much for all workers inside knowingly corrupt industries.
If I'm just stating the obvious, I apologize. I've never yet been privileged to belong to a union. But with the government largely incapable of defying the ultra rich, how else would working people demand any change at all other than by pressuring business? Economic protest is probably the most powerful nonviolent form of protest there is, certainly in a thoroughly subverted democracy. If strikes can only be sanctioned if they won't rock the boat too much, and democracy is only allowed not to rock the boat too much, what's the next move supposed to be? Dying like feudal peasants?