Simple reason - we all know that some players are acting badly and making the game to be less enjoyable due to multiple reasons like:
- Leaving the warzones by the first sight of loose.
- Needing the stuff which aint for them/cant use it.
- acting like premature jespers
- ruining the game experiences for any reasons
- bad behavior in chat
- etc
Now i know that we can report such a player, but honestly, i doubt that BW have time to investigate all reports and act quickly.
This can be even good player feedback for them from a long term.
I am aware that this feature can be abused and can cause alot of bad blood, because some people just like to play a trolls and they will have opportunity to "rate" for no reason, or just because someone beated them in PvP for example.
In my opinion, it can be good to see if this or this player has no "bad rating" and is even dependable, because of "good rating" and most of people with common sense will "rate" fairly if they will want to and from looking at another person "rate" they could make a good picture about the person of which i am going to play with.
Oh yes and I know that my english sucks, so be polite