Coming in from a lore perspective, I can see where there were certain choices made–but made very arbitrarily, from the beginning.
For example, before WoW, night elven druids were only males. They added in lore later to justify there having been past female druids, just that they were rare, etc. But before the game even began, there were restrictions. They decided to discard those for the game, though.
While I love the idea of there being lore reasons for things, they have been, thus far, so shoddily added into the game from a lore perspective (like, we don’t get a story, for instance, on why suddenly gnomes are priests, or why humans finally got to be hunters. Or really any good and meaningful explanation of tauren paladins. Most of those have been fan-created;) that I find myself wishing that they’d added stories for things–or lore reasons. But barring them doing that, just make everything available to every race at this point.
I don’t see it as being a racist thing, either, by the way, since there is no option that is restricted from any player playing it–save that it isn’t offered by the game. And while this is a reflection of where Blizzard has chosen to spend its resources (rather than making new animations for the various races and making sure, if they bring them in from another race, that they work without looking wonky, for instance,) it certainly isn’t a reflection of inherent or subtle racism on their part. I imagine it’s just a time, money, and resources issue.
But I will still wish there were some good story explanations for various things, even if those explanations were just, “This has existed for a long, long while, but until now, none of them wanted to join the Alliance military. But now they have! Yay! We have hunters in the army now!” …or something. It would help every race and class get a good feel for where they came from–a jumping-off point. But for now, it’s mostly left up to our imaginations. Which…isn’t all bad, either–most of the time.