I think that it is three things. First of all, your sisters and mom sound very insecure. They think that if you don't notice every little thing about them (like their changing moods), then you simply do not care. The second thing is that most people are afraid of rejection, so they don't like to come out and ask for what they want, because they are so insecure they think that you will say no. Third of all, people are lazy; good communication takes effort (you have to think of what to say and how to say it), and most people don't like going to all of that trouble.