Someone chime in and feel free to correct me if I'm wrong, but here's how I understand the "regulation".

The EU decided that having a single standard port to charge a smartphone was a good idea and in the long run, save a little bit of money and a little bit on electronic waste since people would be able to go to any store and purchase for sale 1 Standard Smartphone Charger™ and 1 Standard Smartphone Cable™.

Then they conferred their preference to the Smartphone Industry™ and said "Okay, you guys sort it out. Pick a standard, incorporate it going forward, or we will bring down the regulatory hammer and not even we want to do that."

At that point USB was proving to be more or less a de facto standard anyway, so the industry said okay, settled on that, and somehow Apple got away with being able to just bundle in an adapter for the Standard Smartphone Cable™. The benefit of this approach rather than the EU swinging the regulatory hammer is it leaves the industry free to update it, say from micro-USB to USB-C, as improvements come along, rather than the EU decreeing that all smartphones use micro-USB which would be Terrible. Thus we have a Standard by Agreement, rather than a Standard by Law and life goes on pretty okay.

For good or for ill, the EU has a massive amount of soft power in their lawmaking alone with repercussions that go beyond the 28 (soon to be 27 again) member states. Any smartphone designer is free to take their phone and go home, but that's a lot of money to leave on the table and its not like anybody particularly liked the old crappy connectors of the past.