Modern houses have PEX plumbing. It has some advantages over copper, e.g. it won't burst if it freezes. But the main advantage -- it's less labor to install.
Another huge advantage is you can easily do plastic pipe plumbing yourself. You just need one clamping tool, that costs less than one hour of plumbing labour would cost. Plumbing with copper piping or steel pipes requires way more time, skill, and expensive tools.
PVC drain pipes are also simple to install correctly: a tape measure, a saw, and some PVC solvent cement is all you need for simple jobs.
Assuming you follow directions of course: PEX has zero UV resistance and if exposed to the sun for a couple months will break down and be useless.