I've had the opposite experience.  Since I switched to electric the lines are far cleaner.  I wipe them down after each flight and there's hardly any visible dirt on the wiping cloth. Go figure.

I don't see how there could be any electrical effect on dirt on the lines.  It would take voltages in the thousands of volts on the lines (basically, an electrostatic charge), and a typical electrical setup simply doesn't generate that.

It's either something to do with less vibration, or perhaps no fog of oil in the air when you fly.

Evil Malign Forces.....not to be confused with Evil Malign Power

The planes always pick up some static charge when flying.  It's highly dependent on weather conditions.  Warm, dry, and calm seems to make it worse- more static, more dust.
The dust may be coming from how you wipe off your lines.  A clean rag and solvent will clean off more dirt.  Putting any kind of lubricant on stainless lines isn't necessary and will pick up dust.

You can make sure the plane is grounded by making sure you hand has electrical contact with the lines.  The old easy just handles were great for zapping the flyer.  Often one's hand would lose contact with the adjustment loop on the back and static would build up.  The cure was some bare copper wire wrapped around the handle and the adjustment cable.