It is likely to stop people injecting malicious code into the forum now as the issue have probably no been fixed. They have just prevented it from happening by disabling the feature.
Q: Why doesn't the forum let me add an avatar?
A: The forum was hacked some time ago. It is thought that the avatars were used as a means of injecting malicious code into the forum. Even though the vulnerability was patched, the avatars will be disabled until a new forum software is released.
They said something different..