Maybe while looking at the code themselves they found a very bad bug which would make previously made encrypted partitions easily crackable, and fixing it would obviously make the world aware to this, and they don't want to endanger or ruin the lives of everybody who has had a truecrypt container with sensitive data taken from them (for example to a malicious government), so the only way to go for them is to tell people their product should not be used any more and is bad.