There is reason why there is not such feature, and that is relevant for any game.
Too many players at once will spam chat tab like no tommorow, even without dedicated spammers or bots. Chats works as intended when there is optimal number of users connected, but once it gets "populated" too much, it can quickly became ridiculous mess.
Given how many players are at same time online across all game modes, if galaxy-wide chat would be possible, there would be chat spam like several msgs per seconds, to point before you could read anything, it would be already gone due of spam.... just look what is happening on chat at any twitch/youtub livestreams with decent popularity, where is thousands+ of watchers... good luck having actual conversations with someone at these. Unless you are extreme fast reader, it is simply not an easy task.