Hi,
Thats because, the particular account started from Facebook. Later on he/she wanted to start logging in n play from wgt.com.
Now if he/she decides to transfer the fb account to wgt.com with the tier n much more, then wgt will transfer it from fb to wgt.com but at the same time, wgt won't be able to transfer the ranked scores n history. Thats the limitation they have.
Ex: a champ with 0 ranked rounds.
Now in future if anybody want to transfer all the process from fb n start playing through wgt.com with all the ranked rounds n whatever details just like that from fb, all they need to do is just ask for a new password creation. In this case, you get a new password n start logging in n play with all the details exactly from fb wgt playing.
Its all your choice,
1) if you wanted to start the game as new with no records but maintaining the tier n username.
2) transferring all the fb details just like that by a simple password creating with CS.
Now, I see many people seem touchy when somebody ask a curious question. Don't know why its such a big deal !!
-Carl