Interesting point. I wash mine everyday. Water and diluted dish soap. The frames have titanium--but I bet the mounting posts on the silicon pads are the ones that are oxidizing!
I rarely wash my glasses with soap and water, maybe once every month or two. I DO regularly wipe them with a cloth, usually my tshirt. My nose pads have never turned green in 60 years of wearing glasses.
I've had this with cheap sunglasses that use copper screws to keep the pads on. The green is the copper oxidizing. Cleaning them would only make it worse as you're just exposing the copper to water.