Context?

So often (and not only in online text-only conversations, though that's where it's most evident) I get people asking or telling me things as if they were writing me a telegram with their last pennies, so they have to save every word. People particularly love leaving out verbs, but often enough they'll boil down an entire sentence to one noun. This may not be quite as silly as it sounds: if you walk to someone about 12:30pm with a sandwich in your hand on a plate and say "Lunch?" the meaning is fairly evident (the missing words are "would you like some..."). But most people carry around a lot of context and assume that everyone else shares it, whether they do or not.

Which is fine, really. I am even perfectly happy to accept that most people share more context than I do, so most people aren't confused or misled by these extremely short forms of questions nearly as often as I am. The positive-spin, arrogant reason: most people aren't thinking about two other things at the same time, they're only thinking of the one most immediate thing, whereas my mind's bouncing from topic to topic all the time. The negative-side, self-deprecating reason: most people have a native ability to read other people which I was born without.

What gets me though is why people seem so reluctant to elaborate. Ask for clarification all you like; by the time you're at the point of ambiguity, that door is already closed. Once they get to the point where they think one word is enough for a complete conversation, the "obvious" context is no longer on the table, or indeed anywhere near it. They will repeat the one word, or elaborate on it, but they usually seem unable to realize that there were other missing words that they might need to supply. They're already past those.

I merely wonder why people are so chary with elaboration in the first place. No one is charging them by the comma.