Aluminum is common in this type of thing though; some of the biggest names in it use aluminum...
Aluminum is probably common because it is cheaper than copper, thus the markup turns a greater profit.
There is one advantage over aluminum that copper has (though you would want to use copper lugs on the copper wires as well to realize it, or not use lugs at all): less resistance.
When you have a junction between aluminum and copper, the resistance is higher (especially if there is corrosion). If you have enough current running through these junctions, they can overheat, and cause a fire.
This probably isn't a big concern in car audio, except in extreme installs of high-power amps and such (and at that point, copper is cheap, I suppose), but in a house it is a big concern. Back in the 1960s and 1970s, houses were constructed which used aluminum wiring, because it was cheaper than copper. However, a lot of appliances (lighting fixtures and such) used copper wires. Twisting these wires together and attaching a wiring nut is the common method of connecting the wires mechanically. Similarly, these wires were also connected to the brass connections on the sides of wall outlets. These mechanical joints had a much higher resistance than if copper wiring was used. In normal usage, this wasn't an issue, but as the current needs went up, these joints could become very hot - hot enough to start a fire.
I live in such a neighborhood (on the west side of Phoenix); my own house, long before I bought it, actually caught fire in such a manner (and was rebuilt, with the wiring replaced with copper). These houses are all 30-40 years old now; generally, if you hear or see a fire in a house on the west side of Phoenix, generally it is likely to be due to this kind of electrical work. I can't really lay the blame solely on the builders; more often than not, there is also an element of the homeowner running at or beyond the capabilities of the circuit, and not understanding that in relationship to this kind of wiring; but using aluminum wiring doesn't help.
I also tend to wonder if we won't see something similar in the future, simply because copper has gotten very expensive compared to aluminum - I'm sure there are new homes and other buildings wired with aluminum, and people are likely no more informed than they were previously about the issue...