Why are not all metals included in the reactivity series
It's a good question: "reactivity" may vary depending on concentration, temperature etc. but should generally closely approximate the electromotive (galvanic) series.

That said, as @Karl mentions, reactivity series I've seen usually are incomplete, often leaving out transition metals with multiple valences such as Mo and W. To fill in the missing species, look at a good table of the electromotive series.

The omission of so many metals is downright shocking, revolting. One would think a current table would have included more metals; these reactivity series seem like works in transition.