Well, the search function will reveal a zillion threads, most of them of the "maximiser" type. The most important one was mentionned above.

A) The van is gone since 2+ years, you will have to walk and lug your bags ( no carts )

B) You will arrive in B ( a new stupidity for ex ZRH pax introduced by FRA airport management).

C) No need to go to FCT when you can use the excellent lounge in B, food and drink selection is as good as at the FCT without the hazzle of trecking from B to the FCT.

D) If you need the limo drive for your ego or for convenience, they will also provide it from the B FCL to your A or C gate.