For the exact same reason why you can’t covert Orbs of Growth into Orbs of Anything.
They’re a critical cornerstone of the modern GoW economy, and aren’t going anywhere anytime soon, if ever.
Partially quoting myself from last week on a similar post:
Simply put, if a player could trade up treasures, even at atrociously bad rates, then eventually players will be able to realistically raise a Hoard high enough to clear PF 500 without Tuesday/New Faction Event Potions and/or buying out substitute 3k gem cosmetic pet days.
And that’s not happening anytime soon, if ever. And if that day ever comes, there will be a replacement game mode that has the exact same issues already implemented in the game as the next major player nigh-unscalable roadblock at Power 20+.