Many serious Modern players are going to want complete play sets of this entire cycle for their quiver, and Commander players will find reasons to want them too
I also like that both Questing Druid and Virtue of Loyalty are great fits for this game plan on their front side, helping the deck to go tall and even threatening to steal some games with the fun-of Voldaren Thrillseeker
A handful of buyers have bit the bullet on the double-digit prices for this 13-year-old Common, presumably to bling out their Commander, Pioneer, or Pauper decks where Hidden Strings can combo off with Lotus Field or High Tide
Sapphires secondary theme is items matter
For a single instance of damage, you can create a 2/2 flier for hard-to-block damage
If one other Merfolk is tapped, Kumena can't be blocked that turn, allowing it to reliably deal commander damage