Because it's extremely situational and doesnt let her counter mages or dragons. All the other enemy types listed she already counters, having distant counter let's you counter literally anybody, all you are giving up is a +5 stat buff to atk and def.

Rinkah only gets use out of countering bows and daggers, and the foe has to attack or she has to be at full health. Like theres just so many factors that have to align for the skill to get it's full value and too many limitations for it to be worth using over distant counter.

You could easily run distant counter and brazen atk/def 3 as a seal and actually get a better buff that is easier to meet the requirements for because all you have to do is be at at least 80% health.