Originally Posted by
DogHead
"We manage award availability on our Star Alliance partners just as we do with United's own saver awards," said Jeff Kovick, a United spokesman ... "It is an ongoing balance of ensuring we meet our customers' interest in award travel on partner carriers with United's need to generate revenue on our own flights."
So there you have it... from the horse's mouth.
Btw, recently I've also seen the reverse problem. Flight (small feeders inside the US) are avaiable as UA saver awards, but not for redemption with LH miles and not visible on the ANA tool either.