Mood, needing to think on a reply, not being able to tag everything but wanting to hit as many players as possible, whatever. There are a jillion reasons.
it's okay. It's really weird to be on the receiving end and wonder, did they forget about the other one? Did they not get the notif? Is something wrong?
I have one of ours in my inbox. The problem is it is actually kind of weird jumping between the combat and the emotional, so I may boomerang one or the other more. xD