Grigoris, a couple of thoughts...
Gordīs coment about anaerobic circumstances is is meant to point out that stainless can suffer corrosion in applications where its exposure to sea water is absent sufficient oxygen. OTOH I think this isnīt a problem for stainless chain because it mostly lives in a relatively oxygen rich environment (chain locker). As to why marine vendors sell it if s-s chain isnīt suitable, the answer is always because they can make a profit, whether it "makes sense" or not.
FWIW I was strongly encouraged to avoid using a Wichard s-s shackle
between my galvanized rode
and chain because, the chandler claimed, it would inevitably lead to failure of the shackle
due to corrosion. This was in an established Falmouth chandelry and from a pretty experienced mariner, so it left me somewhat cautious.
Iīm wondering: has anyone experienced a failure of a stainless component, used in a galvaized series of anchor