According to a couple of online English dictionaries, “hiatus” comes from the Latin verb “hiare”. One of the dictionaries says “hiare” means “to yawn”. The other says it means “to gape”. Although yawning and gaping generally require an open mouth, it would be difficult to yawn (from boredom) and gape (from astonishment) at the same time.  

A yawning gap, as opposed to a yawning gape, suggests a larger opening than anyone could achieve orally, even Joe E. Brown:

Or Carly Simon:

But a hiatus need not be yawning. It can be extended or brief or neither of those. One thing it can’t be, however, is permanent. A permanent hiatus isn’t really a hiatus at all, since a hiatus, like an open mouth or a yawning gap, requires boundaries. 

Announcing that one is going on hiatus, therefore, implies that one’s departure is temporary. For a blogger, a hiatus amounts to being closed-mouth for a while (despite the fact that being closed-mouth, even for a brief time, is the opposite of yawning or gaping). There is an implied promise or prediction that you are going to open your mouth again. If you don’t resume blogging one day, you haven’t been on hiatus. You’ve just stopped.

Ok, I’ll stop now.