>>532593123
There are a lot of decks that are varying levels of good that just never see the play they deserve for one reason or another. Maybe it came out in paper at the same time as something that overshadowed the whole game, maybe it had a terrible first wave and nobody updated their idea of the deck after the second wave saved it, maybe it was rogue viable but nobody was willing to prove it, etc.
As for Pure Melodius, I don't know. I'd guess that in part it got overshadowed by its use as an engine which colors peoples perceptions of the deck as just being slop that's not quite good enough compared to other slop.