Around one golfer in fifteen plays left-handed, and left-handed in a senior flex is a narrow slice of an already narrow market.
That is small enough that filtering to senior alone would often leave this page empty, so it deliberately includes regular flex too, and every card says which it is. The practical consequence is that you will sometimes choose between a club that fits exactly and one that is a step stiff but better in every other respect.
The ranking makes that trade explicit rather than hiding it: a flex step costs about as much as the loft band is worth, so a one-step-stiff club has to be genuinely better elsewhere to come out on top.