Each country still mandates specific plugs.

And yes, if power delivery was still a relatively new industry, EU absolutely should have mandated a single universal outlet that's "good enough". But existing designs predate EU by decades and are already so well-entrenched that changing them all to standardize on a single plug is too much effort to justify the gains.

But it ain't so with USB-C. Mobile rechargeable devices are a relatively recent tech, and the market has already largely converged on a single design. At this point, making it into a real standard, with the result that it's guaranteed to work everywhere, is a no-brainer.