Early-set nostalgia : As OPTCG matures (now 15+ main sets deep), the earliest sets carry historical significance similar to base-era cards in other TCGs
Along with the above requirements, some Pokemon, such as Raikou V, have a draw Ability like Fleet Footed that requires the Pokemon to be in the Active Spot to use their Ability
Dromar's Charm is a decent example of this providing you with a hard counter spell when you need to protect your board or stop someone from winning the game by providing five life when you're falling behind, or a little -2/-2 to take out a utility creature
If you're sure it should still be valid, be sure to check you've typed it correctly - MTG Arena codes are case sensitive so be sure to type them carefully
experience, with all the rules and cross compatibility between platforms
Its just one triggered ability away from being good instead of okay, but then again its an uncommon, not rare