Why would a reasearcher use a primary source instead of a secondary source when analyzing a historical event

A primary source is more reliable than a secondary source since it’s from someone who was at the event or from that time.

2686-2181 bce-- "egyptian civilization developed along the nile river in large part because the river’s annual flooding ensured reliable, rich soil for growing crops."

1069-664 bce-- "ancient egyptians developed wide-reaching trade networks along the nile, in the red sea, and in the near east."

religion played a major role in the american revolution by offering a moral sanction for opposition to the british--an assurance to the average american that revolution was justified in the sight of god. the revolution strengthened millennialist strains in american.