BitLocker lacks another one of TrueCrypt's most important features: open-source code, readable, verifiable, and compilable by any interested user. BitLocker is almost definitely already backdoored, so encouraging people to switch to that makes all of that data accessible by the powers that be.
I think it's silly to pretend like no authorities would have an interest in promoting the use of closed-source encryption techs. Apple and Microsoft were both willful participants in the PRISM program. TrueCrypt was the only open-source FDE software that had widespread adoption on non-Linux systems. After this, no major corporation or group is going to use TrueCrypt to encrypt anything anymore and will rely entirely on the backdoored encryption solutions provided by the NSA's known and confirmed compatriots.
How would a software with closed source from a company that has been gladly working with the US government in the past be a "viable alternative" to TrueCrypt? Really, please try to read the comments above before you enter the discussion.