One of the biggest problems with mana ramping creatures is that after a certain point in a game, they're not very useful
This isn't to say, by the way, that opening boosters currently isn't fun
Its trending upwards, its sold out of Card Kingdom, its underpriced on TCG Player, its an artifact, its the 7th-most-played equipment on EDHREC (Greaves, Boots, Clamp, Sunforger, Whispersilk Cloak, Sword of the Animist), its tricky to reprint, its the 11th-most-played card in Dominaria and, most importantly in my opinion, its in all 4 of these decks because people are figuring out that its a better Conjurers Closet in most decks and anything that scales off of the number of creatures you have or number of creatures in a tribe wants this
This particular Trainer card is one of the only Stadiums in the expansion set, and it holds a lot of competitive potential