Government taking credit
The thing when governments manage to get businesses to do things, and make a big announcement, is that it's often something business is going to do anything because of business development, and the EU taking credit for scrapping roaming charges is one of these things.
Before their announcement, Three had already scrapped roaming charges, so if Three could do it, presumably everyone else could. And this was partly about one company gaining a competitive advantage, but also that the value of roaming had collapsed. I knew someone who was doing business around Europe and switched from making calls on phones to buying hotel wifi for £5 a day and using Skype. He reckoned his bill fell from over £200/month to around £30/month.
If roaming was introduced by a company they'd gain nothing. Even if all of them did it there would be little advantage. People would just use cafes in Magaluf or Paris to upload their data.