It's because it allows players to drain life from opponents
It is also why black is the most common colour alongside blue in legacy and vintage where you need to have some interaction with spells and their potential to be cast so as to not get run over by broken things
Many Mint cards, once graded, can reach PSA 10 Gem Mint, dramatically increasing their market price
Those who want to complete their sets can do so without shelling out the big bucks
Thanks to this, according to EDHREC, Alela, Cunning Conqueror appears in around 64% of Maralen, Fae Ascendant decks right now
The artwork of this card is arguably simpler than some other Illustration Rares, focusing on Infernape itself with no real background to speak of