They have rules that span multiple games, which is problematic for single-game multiplayer, are variants of cards already banned, or are too nightmarish for even us to contemplate: Once More With Feeling R&Ds Secret Lair Richard Garfield, Ph.D
Shanids effect isnt bad, per se, but its just not as flashy as Dihada as your Mardu commander of a legends-matter deck
It comes with the clause that any mana can be used to cast it as well, making this card a bit better than some others with a similar ability
And then you cannot sacrifice the Goat for mana for free, just like you can the Prism, you have to tap the Pasture and then sacrifice your Goats, and since it taps for mana, you'd need to sacrifice two Goats to make a mana
That's how enamored we are with Vampires