Why were least reactive elements discovered before more reactive elements?

Answer 1

The simple reason is that least reactive elements are mostly found in their native state while reactive elements are found in combined state (in form of their compounds). It is easier to extract any element in it's native or elementary form. Such elements can be easily separated from their ore. They are separated by using physical processes. Reactive elements need to be extracted from their minerals through chemical processes which are more expensive and tedious.

Answer 2

Least reactive elements were discovered first because they occur naturally in their pure form, making them easier to identify and study. More reactive elements tend to be found in compounds or ores, requiring more advanced techniques and technology to isolate and study them.