The top poster's wife is correct. Electronegativity is the key. It seems kind of intuitive, but very difficult to explain.

One definition is that metals can conduct electricity - as in exchanging electrons.

The periodic table is two dimensional. The vertical axis or rows tells how many shells or layers or orbits of electrons an atom has. As we go downwards in the table the exchangeable electrons are positioned further away from the protons, so the electrons are less attached and more likely to be exchanged by close proximity of other atoms.

The horizontal axis is the number of electrons in the outermost orbit. The rightmost ones have full outer orbits and don't have vacancies to exchange electrons, but as we go left, the atoms are more and more short of electrons to fulfil the outermost orbit = electronegativity= missing some electrons.

Combining this shows that the atoms most likely to exchange electrons are in the bottom left corner of the table, which is also the previously mentioned definition of metals.

Someone else pointed out that the actual distribution of atoms is very much not metallic. In the entire universe there is 73% hydrogen, 25% helium and only 2% of everything else including all metals. Even on a planet consisting of "everything else" very much, it's still rare to come by metals, hence their value.

The reason why metals take up so much space on the period table is simply that metals have a lot of different configurations which need to be described because they are different from each other.