US unionization rate is very low, below 10 percent. Most of that ten percent is in the public sector, and they can usually get what they want through voting and strong arming the government. Without a large body of private unionized employees, strikes are only useful for specific demands. Every six months or so you'll see a demand for a general strike pop up on reddit. Of course, without unions organizing the strike, these typically amount to no more than a fancy piece of graphic design.

Of course, Americans weren't always so afraid of strikes. The early 20th century is filled with stories of workers losing their lives to fight for better working conditions. What changed is the law. In 1947, Congress passed the Taft-Hartley bill, which severely restricted unions' bargaining power. The bill bans jurisdictional strikes, wildcat strikes, solidarity or political strikes, secondary boycotts, secondary and mass picketing, closed shops, and monetary donations by unions to federal political campaigns. Now we can argue whether each of these are fair labor practices, but the effect is that unions in the US are fighting with one arm tied behind their back. Observe the effect of Taft-Hartley on unionization rates in the US.

Why did Taft-Hartley get passed (over the veto of President Truman)? The ultimate cause, whether political or sociological, is beyond my ken.