Galvanized pipe is rarely used. According to the Copper Development Association, copper tubing is used in about 90 percent of residential potable-water systems, with the remainder of the market divided between galvanized steel pipe and plastic pipe and tubing. The labor costs are greater to repipe with galvanized compared to copper. It takes longer to thread steel-pipe joints than to solder copper pipe. Also, a plumber can bend copper tubing for a slight change in direction.
Galvanized pipe requires installing a series of fittings to change direction.
Furthermore, my experience with galvanized pipes, as a home and building inspector for the past 25 years, is that it will last about 50 years. Toward the end of its service life, however, water flow to the fixtures is decreased because the pipe is clogged with deposits. Copper tubing has a history of providing a service life of more than 60 years. Nevertheless, a small percentage of copper pipe and tubing experiences premature failure when pin-size holes form in it. Incidentally, plumbers generally guarantee the quality of their work, but not the quality of the copper tubing.