Planck observations of thermal dust emission reveal a maximum polarization fraction ($p_{max} \sim 20\%$) that is significantly higher than earlier predictions, implying a high degree of grain alignment and magnetic field order. However, the polarization fraction drops systematically with increasing column density ($p \propto N_H^{-1}$ or steeper) in dense clouds, often referred to as "polarization holes." Standard alignment theories (Radiative Torque Alignment - RAT) struggle to fully explain this rapid depolarization solely by optical depth effects (loss of aligning photons) without invoking significant tangling of the magnetic field on small scales or changes in grain physics (growth/coagulation) that are not independently constrained (Planck Collaboration 2015; Ritacco et al. 2025).