People from USA all speak perfect english and can communicate together perfectly, they also understand eachother like i understand people from my own country cause they speak the same language.
Not all from EU is that great in english to have an actual conversation together with other players while playing the game and focusing on winning aswell.
When they don't do callouts in EU, i dont know why they wouldn't, maybe they're shy to speak english on mic? lol. I see your point in that, a lot of people type callouts instead of actually saying it, and you don't have the time to read chat while taking over a site etc. I don't experience the lack of callouts on mic in higher ranks, only when i'm smurfing.
Personally i enjoy the silent EU envirement, aslong as they do callouts, i would pick EU > NA anyday in MM.