Well, plumbers may find some plastics easier to install. But consider the reasons favoring copper. Copper meets or exceeds building codes in all 50 states. It's governed by strict, long-established standards and is permanently identified for home inspectors. 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.
Copper is rigid, it doesn't sag over long runs and requires few supports. Copper will withstand more than 1,000 pounds of pressure, even though normal system pressure is about 50-80 pounds per square inch. Copper tube and fittings won't embrittle with age, so they can't crack or crumble years after installation. And they can endure repeated freeze-thaw cycles, although, of course, no plumbing should be allowed to freeze. An open flame or electrical resistance heating can be used to quickly melt frozen water in copper tubing, because copper has superior thermal conductivity.