Let's not pretend that all companies are cash-strapped startups. The FAANGs of the world and the Fortune $x companies and the multinationals can absolutely afford to pay their global workforce uniform wages, but they choose not to because it's not maximally profitable to do so.
I'll contest that. FAANGs are extreme outliers. I can assure you my company, while it certainly can pay everyone an extra, say, 10%, definitely cannot pay all its SW engineers Bay Area salaries. And then Non-SW engineering companies - even the top ones - rarely have that much money. Their operating expenses and capital costs are a lot more than a SW company's is.
That does not really make sense. Work does not have some inherent value, its value is based on market situation, and different markets have different price equilibriums.
The outcome is that Bay Area folks will get paid less than their current pay, and those in India get paid more than their current pay. Because there's no way my company can afford to pay all their developers Bay Area rates.
That would be using exactly the same rationale as your comment: Equal pay for equal productivity.