Metal Pokemon cards sell for between $20-50
Both are Level 5+ DARKs, which add synergy with the Resonator package, but Ebon in particular is both Level 7, and benefits from destruction, meaning Gandora-G triggers that extra effect, essentially adding another layer of protection for the strategy in the form of a free Turn Silence
If you run this out with Prossh, Skyraider of Kher, 49 of the nonland cards pretty handily go with the plan, while Shattergang Brothers only want about 29 of them
On top of that, it grows even larger whenever instants or sorceries leave your graveyard, so its an incredibly strong card, especially in multiples
The reason it sees so much play is that it is doing two things that are well paired, both stalling the game and it is never a dead or even that weak of a card in any given matchup
Uninspired it may be, but these cards are actually sneaky strong