For me, engaging takes SO MUCH energy. Its like starting a cold engine. Once its running, its fine, its fun, but starting it up, OMG! So if you call randomly, you could be calling while the engine is off, or being taken apart for repairs!

Is it not just basic politeness for us to respond? Well, if we had been raised with basic politeness, it would be in our repetoire to do so, yes. But its not.