Metal is far denser than wood is, and although wood is the traditional material for a flute, it does not provide a clean sound that can be projected easily. The shiny metal used for concert flutes are also very appealing to look at, as well as being much more durable than any other type of material.
It should also be considered that beginners are often young players and can be rough on their instruments, using a durable material can keep an instrument from being destroyed.
Concert flutes are made of metal because the denser the material, the better the sound the instrument makes. Metals make less difference in sound quality, so any metal flute is an excellent instrument in concert. Flutes made of metal can also be designed and assembled to differing specifications.
Also, shiny silver metal is far more appealing to the eye. Concert flutes made of metal have a high, bright sound. The sound of a metal head joint can be described as cleaner, sharper, and more focused. Also, metal flutes are far more durable.