LH choose the Kempinski because they had some company connection years ago. I slept there once and I can say even the airport sheraton in FRA is better after the renovation.
I really dont know why they send the customers to such a remote hotel which is, besides some suite, not state-of-the-art. Maybe it is just because its cheap, and this shold not be the attitude towards F guests at all. If they want to save money, maybe they send us to the LH training center in Seeheim-Jugenheim (30 mins from the airport) which is also bookable via some hotel booking service. Small rooms, no TV etc but very nice sporting facilities and only young people at the bar (LH staff) THEN they REALLY save money !!
Especially at daytime they can tell their own people to take out all their personal belongings at daytime to make space for F pax who want to use a shower.