Because for Arcane we were kind of confused how to play around Prismatic Crystal with it being on 1 minute cooldown, while Evocation and Power are 90 seconds. Would it be better to use it on cd or delay or whatever. With all of it being 1.5 minutes we can line up burn phases with PC every time. For Fire I suppose it's because Combustion is also on a 1.5 minute cooldown. It's not necessarily a buff, but it makes gameplay more logical and fluid and being able to line it up with our main cooldown kind of constitutes calling it a buff.