Roaming works but why still so many apps?

I just got back from a trip through three EU countries and the charging itself was fine thanks to roaming. But I ended up with five different apps to start sessions, and two of them required prepaying a balance I still haven't used up. With all the talk about Plug & Charge and interoperable networks, why are we still juggling accounts and apps depending on which country you're in? Is there a simpler way you guys are handling this, or