Not trying to be that guy, but what would be the difference if these allied races required you to grind current content? Unlocking HM tauren / Nightborne / Void elves / LF draenei is actually easier (story quests give more rep, WQs give more rep, there are more weekly quests with rep for VE / LFd than DI and Maghar, and the rep tokens are a lot easier to get).
If you didnt know that you even have to grind something to get them, its on you for not getting the information. The fact that blizzard doesnt advertise them as new races, but as allied races, already points that something is different.
As for "old content to unlock them" debacle, IIRC blizz is already planning to make the rep grind a lot easier in 8.1.