Why does the strongest accent usually fall on the first beat of a measure?

In metrically organized music, it is actually the presence of the accent that determines where a measure begins, rather than the accent occurring because of the measure's start. The heaviest accent is placed on the first beat to articulate rhythmic groupings and provide a clear framework for metric articulation.12

This primary emphasis, often referred to as the downbeat, serves as a foundational reference point for performers to maintain consistent timing and structure. While this pattern is standard, these regular accents can be temporarily displaced through syncopation, where the expected stress is suppressed or shifted to create rhythmic interest.134