Everyone is probably missing the whole point here.
Upwork has the data, they know how happy the client is after a contract ends, they know the expertise level that was required by the client when opening the job, they know the hourly rate that was charged (or fixed price).
It's extremely easy to cross all the data and find patterns to understand what's needed to a successful job.
I'm not saying Upwork should block someone from applying to a job, or should only allow the client to hire within specific rates.
It's just that, if you want an expert, you CAN'T add that you want to pay $5/h in the job description.
Maybe tweaking the fields, the copy, to make it clear that experts cost more than $5/h, and give clear price ranges. Do you want an expert on data science? Ok, that will cost you $200+ per hour.
This would be helpful for clients to set their expectations, this would be helpful for freelancers who will more clearly understand how much the client is willing to invest.
It's so simple...
Ok, I've got your point.
I think that something similar already exists for freelancers when applying for a job. They try to "increase rates", but honestly it does not look it works. I never got a job, when followed UpWork's suggestions
I do not know if something similar already exists for clients or not, but I think that UpWork may be not interested to suggest clients how much they have to pay. Here is not a socialism, and every client/freelancer should know when he/she get for a rate. If a client whats to pay 5 dollar and get a freelancer the Upwork gets percentage. If Upwork request he must pay 20 dollars, he will leave the platform without hiring. And I think hour rates are not such problem here, then hiring rating ...
Anyway ... I know for a project where 10 entry level people are developing it for 18 months and still not finished. I am sure that such project should be finished with 3 good developers in 6 months. But yes, good developers are maybe 2 or 3 times more expensive per hour. But start calculating now ... 5*10*18= 900, but 15*3*6=270. So you can see which way is cheaper, but explain me with what words you will convince the client that more is less