Because using Substitute + Explosion Gengar to lure in Blissey and OHKO with Explosion to prepare an Offensive Suicune sweep isn't a viable idea anymore, right?
Ironically, the Substitute + Pain Split is a more reliable way of dealing with Blissey. Lee is right, if all you have is Explosion on your team to deal with Blissey, then your team sucks. Things like Toxic Spike and Pursuit support, mixed attackers, physical attackers, etc, are far more reliable and allow your team to execute its strategy without relying on the opponent not having Protect Blissey + Ghost. People often Protect on stuff like Heatran with Blissey to check for Explosion, so the Heatran will Fire Blast thinking they're outpredicting them. In comes Gengar and well.. there you go.