You can still use your old and hard earned titles even if you decide to play a different class or character at some point
Rank 1 is much much easier on Horde, so you can get it on Horde and still use it on your Alliance characters without being limited to your Horde characters
The title is rare enough as it is, might let those that earned it use it on all characters just like the gladiator mounts.
reputation or influence arising from success, achievement, rank, or other favorable attributes.
distinction or reputation attaching to a person or thing and thus possessing a cachet for others or for the public: The new discothèque has great prestige with the jet set.
adjective
having or showing success, rank, wealth, etc.
So my opinion of this is when you gonna see player with that character with that title, if you make it account wide you will loose the prestige of being impressed by his effort.
Let’s imagine i’m a shadowpriest R1 and got the title.
What sense it will make on a arm warrior when i have 0 clue how it work and never use mortal strike.
The title will mean nothing on the warrior. Instead it will make the title loosing his sense.