I guess some people just don't care. Or who know we have no way to see the last time they logged in. For all you know you could be sending a message to no one!
I agree with you blufantasy, not even for that fact that it would makes things faster but you would think its a matter of common courtesy.
Even a no thank you I'm not interested would be nice.
Another reason is that you need to have the available credit to read and reply, so it could be unavailable due to no funds the wife won't know about. Not mine but you know some ppl are.