I do this because I don't consider online conversations the same as face to face ones. At home, surrounded by work and distractions, it just doesn't seem reasonable to expect that people are going to always be prompt, attentive, and have nothing else that they're doing or obligated to pay attention to while typing about video games or the weather.
This is why I accept very few people onto my messengers. I always multitask because chat is rarely stimulating enough and I fill my life with a number of things that need to be done. Food on the stove won't stop cooking and my bird (when I bring her home) won't stop getting into things while I tell several people I'm stepping away. I don't want to be someone's evening entertainment, I just want someone to exchange messages with as able when we're sitting at home studying, working, or reading for a bit of distraction and company.
If I wanted something else I would visit people offline or have a Skype voice/video call.