Forcing each opponent to sacrifice a creature or allow you to create a Zombie token is no small thing
Maybe theres a Commander deck thats interested in this equipment for the synergies alone, like lowering the cost of the spell or auto-equipping
"The goal of this new 'London' mulligan is to make games where one or more players mulligan more competitive, especially in cases where players mulligan an unequal number of times", wrote MTG developer Ian Duke in a 2019 blog post
I think this only makes the cut if youre doing counter shenanigans, are deep in on Clerics, or are consistently finding ways to make tons of black mana but not the cards you cast with it all
MTG - Duskmourn: House of Horrors Play Booster Display (36 Packs) - EN
There are, of course, weaknesses to a mill strategy some players include cards that prevent themselves from losing to an empty library, like Ulamog, the Infinite Gyre