Not only because its a great budget option, but it also has a lot of synergy with black strategies
At sites like printingproxies.com or mtgproxy.com, you can buy a proxy card for prices around $1-2 each, and it gets cheaper if you buy them in bulk
With many things going digital, its possible to find these at antique stores or other such places
Most sets have a draft common common or uncommon that can repeatedly inflict one damage on each opponent just by playing other cards, like Firebrand Archer or Erebor Flamesmith
Black is interesting because it can be both an aggressive color or a controlling one
Greel, Mind Raker Greel, Mind Raker strikes me as the worst horror commander because its discard ability targets a single player, and thats ineffective in EDH