2FA is apparently fairly difficult to integrate into SMF (the current forum software). There was even a bounty created to crete a 2FA system that is good enough for theymos to implement, however the current forum still does not have/use 2FA.

It is my understanding that one of the requirements for the new forum is for 2FA to be available, so once the new forum is officially rolled out, 2FA should (at least in theory) be available for everyone to use.