Not always....Tempest titanium Commodore is less expensive than their steel Viking with the same movement.
Titanium is completely inert while SS still rusts and oxidized. Even if the 904L is more resistant than 316, it'll still rust given enough sweat and salt water. Also, Ti alloy can be treated to be every bit as hard as SS while still being much lighter.As others have already pointed out, there is no need for a titanium submariner, they already covered that base with the Tudor Pelagos, which is a very popular model. Why have your own models competing against each other?
Rolex is not a company that follows the crowd, it does its own thing, and does it well. While everyone else is releasing titanium versions, Rolex will keep the sub stainless steel, and the steel that Rolex use is better than any titanium, so why bother?
I hope we never see a titanium Submariner.