Why is the Magnetic Needle Of A Compass Made Of Copper ?

They are not made of copper. Copper is not a magnetic mineral, and thus would be useless for anyone trying to find north. Generally, needles are made of iron, sometimes with manganese alloys. The copper appearance comes from the needle being coated with a very thing sheen (only a few angstroms thick) of copper, preventing degradation of the iron needle itself.

On extremely high-end scientific compasses such as my Brunton, the needles exist within a vacuum, so there is no need for copper, and it is more accurate, being able to swing more freely and with more precision. My compass is even magnetically shielded, so I can hold it right next to a giant lodestone, and its needle will still find proper magnetic north (and proper geographic north when compensated for declination).

I also have a Silva Ranger, which is of good quality as well. It does not use a vacuum, but rather a non-oxidizing, very light oil to surround the needle, so once again, copper is unnecessary.

But that's what you're seeing, at any rate.

Needles are made of iron, because copper is not magnetic. However, they are weighted with copper wire, so that near the magnetic poles, they don't point down into the compass.