Can someone explain why this is so valuable?
the stamina mod is useful to get to 210 stamina (so you can use a composite bow or soul glaive at max speed)
dex is capped at 150, above that you must use stamina.
If someone wants to use mace and shield, or some other non 10 stam piece on armor then stamina on jewels is needed to reach 210 stamina.
to expensive for myself, but yes they do hold high value to some people.