When you're talking about better paid jobs you're right to point that out.
But for the bottom of the barrel jobs this doesn't hold and you can check by looking at the salaries for these jobs in the countries that can't offshore further. They're still dismal.
The real reason is that the people looking at these jobs have no negotiating power whatsoever. They have no essential irreplaceable skills or experience, nothing that's hard to find on the market. All they have usually is the desperation to do any job to make a living. They need that salary now while the company can beat around the bush with the service, throw AI chatbots at it, allow longer call queues, and so on.
If anything, a the offshore employees have more leverage with their employer because they need to speak some foreign languages to interact with customers. They can differentiate themselves from the sea of other people in their own country. A US employee in a US call center serving US customers doesn't even have that. Not that much different in Canada despite the bilingualism situation.
