I'm guessing there was big US client demand for this otherwise what would be the benefit for Upwork for doing this? Perhaps clients getting spammed by those that don't meet their basic requirements.
From my experience as a client, 90% of the spam proposals are copy-pasted so they could simply filter them out.
They could also reduce 'connects' (freelancers have a maximum amount of points they can use to apply for jobs. You can buy more points).