As long as we're living in a global economy, it's always going to be relevant; if you understood what was said about supply and demand in a normal-functioning market, then you wouldn't be talking about Upwork enforcing a minimum.
Who is Upwork to decide what the value of something is? It's just the platform connecting freelancers with clients. They don't set rates, both parties do.
The platform is not to blame, it's poorly educated freelancers who are unable to sell themselves to the level of their skills. I've touched on this in my earlier comment - clients will happily pay more if you, a freelancer, justify why they should pay more. Most freelancers can't do this, so they're 'stuck' with low paying jobs. Why should anyone pay more than what they think something is worth? You wouldn't do so in your day-to-day; why expect others to?
The reality is this: you're dealing (mostly) with business people. You must outline your value with what you do. If you can't do this, you can't charge 'what you're (arguably) worth'. You're also 'competing' with the world. If you can't justify a price that stops you from being 'undercut', then you're not being competitive in said global marketplace. If you want to have a 'minimum' payment, go and work in your local market and you'll be pleasantly surprised that the 'minimums' are what you'd expect; otherwise, throw that concept out the window.
Consider from the other side of this - you're a business owner in a developing country, and you're looking to hire someone online to help your business. You do okay locally, but paying rates from a country like Australia wouldn't be possible, so the 'lower' rates you can find on Upwork allow you to hire others and still be profitable. Suddenly, a 'minimum' is enforced - likely from a developed country's minimum rate (they're always the ones complaining about it...) - and you're no longer able to hire people at all because it's cost prohibitive. So you're idea to make Upwork 'better' really doesn't help the vast majority of the world - just freelancers who struggle to justify their value against a global market... read: those in developed countries).
Upwork has no obligation to enforce minimum rates for anything, because rates are negotiated between parties. There is nothing wrong with the Upwork system and it's certainly not to blame. Blame uneducated freelancers.