I guess it’s mostly a matter of time, or rather, the lack of it. There also might be issues with the license of some of the encryption algorithms; DriveEncryption has to use the TrueCrypt license. I’m not sure, if that has been discussed yet.
I improved the situation a bit in recent months, at least it should now work fine in 64 bit as well, and compile with GCC 11, and I’ve also separated the encryption code better from the driver code.