I realize why they do it, but it can never work because the n.p.c.'s do not react to me in return. I can talk to them, say things to them, but they will never respond to anything I say.

Thus, the end result is that Gordon Freeman is a man whom many speak to, yet who never speaks back, and no one considers this to odd to say the least. — the conversations thus appear ridiculous.

It worked better with Chell, because others do not that Chell does not speak back, and Chell actually canonically refuses to speak out of stubbornness, so it's amusing to see Wheatley being obviously uncomfortable from the fact that Chell does not speak back and is simply blabbering to fill the awkward silence.