Why isn't there a reason to pay a *A partner (actually not what I'd call a real competitor in contrast to carriers of other alliances like BA or AF.) to be albe to offer "special" miles of the *A partners FFP? Just one example: A HON (or a SEN willing to achieve HON) is flying a lot across the pond using LH (that's he a uses M&M as his favorite FFP!) and in addition to this he has a lot of inner US travel. Much likely such US travel will be on paid premium fares. As long as UA was offering HON miles this HON (or SEN) would have much likely chosen UA for this US travel. Now that HON miles are gone on UA metal, why should he still fly UA when he could also use AA or DL or US or …? So UA probably lost some premium pax because of not offering HON miles anymore…

Okay, this is just a theory and I can't provide any data or source to prove it. As it looks like you are not willing to accept a theory you can't verify (which is nothing wrong at all) you will much likely refuse it. Anyway it was an attempt to point out that it can make sense to pay a "competitor" to offer an opportunity to gain status in a competitors premium FFP.