Ok, I see, it's only on the Lufthansa redepmtion page. (I was looking all over, because you implied that it was a general AI policy, and that's what I can't find any trace of.)

The site is messed in all sorts of other ways, so I don't know what to think. They claim they're in an alliance, but that alliance has only one other member (LH)????

At any rate, this LH redemption restriction has existed since 2004, and I see no rush by other airlines in other regions to copy it. I suspect it's there simply to "plug a hole" that AI found, similar to the way Amtrak Guest Rewards plugged the hole of AGR->Choice redemptions when they found a "run on their bank" by people who were "washing" CO miles through AGR through Choice onto WN (Southwest).

And speaking of AGR, your account (and all points on it) expires in three years if you don't have a paid trip on Amtrak. Is expiring without paid trips all that different than no redemption without paid trips??

OTOH, I find it very common to have restrictions in FFPs at many airlines in that general part of the world (from at least eastern half of Europe, through Asia), in that they often have such rigid unextendable expriation policies that (as someone from way outside the region who slowly earns miles there mostly through partner activities) there's too much of a risk that I couldn't get to enough miles for a reward before my miles would expire.