Suspicion on the abandonment...
Was one (or more) developers of Truecrypt USA citizens? If so it is likely that they received a secret court order, ordering them to weaken parts of the code or leave subtle vulnerabilities. You would never know as the order would be secret and so in defiance the developers just packed up shop like a well known encrypted mail provider.
If the intentional bug was found for those even bothering to look they could just claim unknown bug and then fix it (and leave another bug elsewhere)
Or simply, they got fed up of coding it.