So I already know that the reasoning behind arena mounts and titles not being shared is that you acquired said mount or title with that class, and that represents proficiency with that class. I think this is fair and reasonable, but what I'm wondering about is why doesn't this transfer to other characters of the same class?

To give a more specific example, I earned Challenger on my first warlock a while ago. However in the late months of 4.3, I made a second warlock on another server, because I didn't have the money for a server transfer. This 2nd warlock is now 90 (the first is still 85, he's on the shelf), and it suddenly occurred to me to see if he had Challenger, and he didn't.

So I have to ask, if they represent class proficiency, why don't other characters of the same class share titles or mounts?