The issue you raise is known as the measurement problem in quantum mechanics, and it remains a subject of ongoing debate and investigation among physicists. The measurement problem pertains to the question of how and why quantum systems, which can exist in superposition states (a combination of multiple states), appear to collapse into definite states when measured.
One common approach to resolving the measurement problem is through the concept of decoherence. Decoherence refers to the interaction of a quantum system with its surrounding environment, which leads to the rapid suppression of quantum interference effects and the emergence of classical-like behavior.
According to this perspective, when a quantum system interacts with its environment, the system becomes entangled with the environment's degrees of freedom. This entanglement leads to the loss of coherence and the emergence of classical-like behavior for macroscopic objects. The environment acts as a measuring apparatus, even if it consists of many microscopic particles, by effectively entangling with the system and causing it to decohere.
In this view, macroscopic objects are described as quantum objects that have effectively decohered due to their interactions with the environment. The description of macroscopic objects as quantum objects is not a circular argument but rather an acknowledgment of the underlying quantum nature of all physical systems, including macroscopic ones.
It's important to note that the measurement problem is still an active area of research, and there are various interpretations and proposed solutions beyond the decoherence perspective. Some physicists explore the many-worlds interpretation, where the measurement process leads to the branching of multiple parallel universes. Others investigate modifications to the standard quantum formalism or the role of consciousness in the measurement process.
Ultimately, while there is no universally accepted resolution to the measurement problem, physicists continue to explore different approaches and interpretations to deepen our understanding of quantum mechanics and the nature of measurement.