It's a natural, environmentally friendly material - not a synthetic. Plumbers know how to install and test it, year-round, through a wide range of temperatures. Since copper is rigid, it doesn't sag over long runs and requires few supports. Copper won't embrittle with age, so it can't crack or crumble years after installation. If, somehow, it does, application of open flame or electrical resistance heating for a brief time can be used to melt frozen water in copper tubing, because copper has superior thermal conductivity.
Copper tubing is non-flammable.
It won't melt, or burn, or give off toxic fumes in a home fire. In houses tragically destroyed by fire, many times the only thing left intact is the copper plumbing. It even maintains pressure when subjected to flames. That's why copper is preferred for fire sprinkler systems. For today's health conscious consumer, copper is almost the perfect material.