It's one thing to allow remote workers from one country to work from anywhere in the world. It's a completely different thing to create a universal and homogenized labour market for tech work.
Universal salaries would allow established and well funded companies to hire anyone anywhere at massively unfair non-local salaries. Individuals would be better off but the job market for equivalent local jobs would suffer and, as a result, new companies in those nations would suffer too.
The difference in purchasing power of the established tech companies in rich nations would annihilate the local labour market competition. It would become next to impossible for non-rich-nation startups to hire the best talent because of the huge opportunity costs potential employees would face. Exporting the benefits of economic privilege like this at the expense of host nations is textbook economic imperialism[0].
Individual benefit isn't the only lens that this issue needs to be examined through.