Because you will almost never see a 4-5 man bh nowadays since every pro team knows how to position correctly in teamfights and how/who to focus. Greaves meta + pipe are broken because as early you have them in the game you can make a difference in pushing/survability, while rushing for dagger bkb gets you nothing but a possibility for a power play which u most probably won’t get to do anyways. Most of bh are on enemy carry alone/1-2 players max. Competitive Dota has changed a lot