How come we can't play with friends from other servers?

Don't get me wrong, this isn't a rage thread. I'm legitimately curious why we aren't allowed to choose to play in another server's queue with our main account so that we can play with our friends who are out of country. The ping isn't always an issue, people make smurf accounts all the time to play on other servers. It just feels like crap to make a friend who's into playing League only to discover they're from EU.

I mean the forums work for everyone no matter where they are, and even a lot of mmos have instances where cross-server grouping is allowed. Is there some huge hurdle that I'm missing here or is it just something Riot has not considered worth implementing?