Tech workers are not the most paid people in a company. The executives are _and_ the company's coffers are at their disposal, especially when the CFO is hyper-obedient.
I can't just say I'm moving to another country, change policy to allow transnational work and give myself a bonus to offset that cost.
Nor can I change the wages of the workers who are underpaid.
Executives and leadership can. With a union, workers have a change to put the needs of the people who *do the ground work of keeping the company alive* to make sure they don't burn out in the process.