I am assuming you mean translate for FK? The same reason that I do not support free rotation on all axes of the elbows/knees is because of IK/FK matching. There is no way to match the IK controls to the FK controls if the FK controls are translated instead of exclusively rotated. If you want, you can unlock the translate channels, but I do not support this in the rig.
Comments on this feature request:
Dustin Nelson said about 12 years ago: