Searches for axion dark matter and gravitational waves are rapidly expanding, with new experiments deploying quantum sensing techniques to reach unprecedented precision. But does one need to account for the quantum nature of the axion or GW itself? I will exhibit two severe obstructions. First, realistic detectors cannot resolve the fundamental modes of a field; instead they couple to coarse-grained "effective" modes, which often washes out nonclassical effects. Second, all nonclassical effects are suppressed by extra powers of the weak coupling, making them much harder to detect than the waves themselves. This suppression applies to all observables, including quadrature and number statistics, entanglement, and decoherence, and rules out many proposed methods to detect the quantization of gravity.