The issue is that the source code is too complex to audit personally. Having no real identity behind it also removes the risk of finger pointing if a backdoor were to be discovered.

"There has been no known comprehensive review of the source code by a qualified cryptographer.[46][44] Thorough security code review and testing is hard, tedious, and painstaking work, and very few people have the skills to do it. There was, however, a functional evaluation of the deniability of hidden volumes in an earlier version of TrueCrypt by Schneier et al. that found security leaks." [1]

[1]https://en.wikipedia.org/wiki/Truecrypt#Reasonable_paranoia