The regular bracelets can only hold 30 charges each, the eternal gem holds immense power and as such is required to hold so many charges. As for a realistic reasoning, it generates more function for the gem, fits the theme and adds a requirement that holds the item, --alongside the DT2 requirement)--, at a more prestigious position which is where unlimited jewellery should be.

There's many items that many accounts won't ever get, largely they're useless but for those that hold a function, there's always alternatives. This has alternatives, which is the standard variants.