Rommath: FAKE NEWS
>.>
In all seriousness, I think once more information is out we get more context on these allied races joining.
Not really both factions had a leader then ended up betraying them and siding with the Legion, they had a problem with addiction to Magic, their society is very Magic based(Like most elves). They sorta got harsh treatment by Alliance(Tyrande being Tyrande, weather you understand her actions or not, it's the same).Mental Gymnastics.