re: "A British writer offering to write an article is always going to be undercut by someone from Bangladesh/India/Nigeria"
Don't you think it is likely that there are British writers who are able to do things that writers in Bangladesh/India/Nigeria can't do?
I live in the United States. Clients from India hire me. They pay my full hourly rate. If the only thing that matters is a freelancer's hourly rate, then why don't those clients hire somebody who is much less expensive who lives in India or Bangladesh?
I didn't say that couldn't happen. Yes, of course there are sometimes clients that will pay more. But that doesn't happen often. Most of the time, clients will happily pay less than the UK minimum wage if the writing quality of the writer is okay.
If a client can pay less than UK minimium wage to get an article written - at the quality that is required - then that is what the client should do. If the client wants to save money.
I don't understand what the issue is.