Blood Elves are too smug to pick up any beliefs or customs from other races - Hell, the guard doesn't realize the Troll Shaman trainer in SMC is a Shaman. He gets confused when you ask, wne he can't tell if the Druid trainer is male or female.
They picked up the concept of the Holy Light from the Humans way back when, which itself requires a great deal of humbleness and submission.
Hell, there's even some implication of the Elves being responsible for teaching the Humans and the Forsaken the way of the Hunter/Ranger. The Blood Elves affinity for Nature has always been a notable aspect of their race.
Them becoming Botanists like Freywinn would be a step backwards for them in society. They'd be treating nature just like they treated M'uru, and see how well THAT turned out...
True, but there are some Blood Elves with a similar mentality that they had in the Burning Crusade.
The funny thing is, is when people talk about Blood Elven lore, I sometimes see them essentially demonize the Blood Elves, considering them evil, while the other half considers they should be paragons now that the Sunwell is restored.
I myself believe that as a people, they are working towards bettering themselves, but there are a few holdouts like their Cataclysm cinematic states. Though through the whole ordeal, there are Blood Elves who retained their honor and their morals the entire time.
Funny thing is the whole thing with M'uru actually worked out great for them, as their Sunwell was restored and the Blood Knights retained their powers.