Just a hunch, but it’s because a) it’s cooler and b) most wires are insulated. It may be that it’s still fluid, but I wouldn’t bet anything on it.
That would be really neat. I’m not sure about how to extrude it well though. I remember someone had a clay extruder, but it wasn’t super fine resolution. Getting a consistent viscosity would be key. I wonder if you could get by manually applying the paint. For example, in the quadcopter part, when it pauses to insert the controller board, what if you just threw in a blob of conductive paint, and scraped or wiped away the excess. I guess I’m not sure you’d get terrific adhesion on the next layer… I’m also not sure how well the paint works to connect to components. That will be something to test before you make a bunch of changes to make a paint extruder.
This all sounds like a lot of fun.