Why did Husserl believe scientific knowledge had forgotten the experiencing subject?

Edmund Husserl argued that scientific knowledge had forgotten the experiencing subject because modern science became preoccupied with an objectivistic-physicalist approach that prioritized exact, measurable data over the immediate, subjective world of experience.

In his work, The Crisis of European Sciences and Transcendental Phenomenology, Husserl illustrated this through the example of Galileo and the mathematization of nature. He observed that as science focused on constructing objective, scientific models, it neglected the "life-world"—the world as it is immediately experienced by individuals. Consequently, the "accomplishing subject"—the scientist themselves and the conscious activities that make scientific knowledge possible—was excluded from the scientific thematization.1

Husserl believed this oversight led to a failed attempt to model human sciences after the exact sciences of nature (naturalism). To correct this, he proposed that phenomenology must "question back" to the foundations of meaning, recognizing that all scientific constructs are ultimately rooted in the constitutive achievements of transcendental consciousness. By ignoring the subject, science lost sight of the very foundation upon which all its meanings are built.1