In most alloy systems, the solid–liquid interfacial energy decreases with decreasing solid–liquid equilibrium temperature, exhibiting a positive temperature dependence. This temperature dependence of alloys on the interfacial energy plays a critical role in solidification kinetics, microstructure selection, and phase transformation pathways. However, recent studies on representative low-solubility alloys, such as Cu–Zr and Al–Sm, have revealed the opposite behavior: the interfacial energy increases as the temperature decreases. Since these systems exhibit extremely limited solubility, there has been speculation that the anomalous temperature dependence of the solid–liquid interfacial energy may be intrinsically linked to their low-solubility. However, the generality of this correlation and its underlying physical origin remains unclear. Therefore, the aim of this study is to determine whether low solubility alone is sufficient to induce this anomalous behavior and identify its thermodynamic origin. Compared with embedded-atom method or other metallic potentials, the Lennard–Jones (LJ) potential enables the direct construction of low-solubility binary systems via appropriate parameter selection, providing a controlled model framework to isolate the effects of solubility. In this study, binary LJ systems are employed as model systems to systematically investigate the relationship between low solubility and the anomalous temperature dependence of the solid–liquid interfacial energy by combining molecular dynamics simulations with the capillary fluctuation method. Two representative low-solubility model systems are constructed by independently tuning the atomic size and binding-energy ratios, thereby enabling the controlled and transparent examination of the effects of geometric mismatch and energetic asymmetry on interfacial behavior. The solid–liquid interfacial energy is quantified from equilibrium interface fluctuations, and the corresponding interfacial thermodynamic quantities are further analyzed to elucidate the underlying mechanisms. The results show that when the atomic size ratio is 1.20 or the binding-energy ratio is 0.60, the binary LJ system exhibits low-solubility behavior, with solid solubility remaining below 1.0 at.% throughout the investigated temperature range. Under these conditions, the interfacial energy increases with decreasing temperature, reproducing the anomalous trend previously observed in Cu–Zr and Al–Sm alloys. Further analysis based on the Gibbs adsorption equation reveals that near the melting point, negative solute adsorption at the interface is dominantly responsible for the increase in interfacial energy. At lower temperatures, the interfacial excess entropy becomes positive and acts synergistically with solute adsorption to further enhance the anomalous temperature dependence. These findings demonstrate that the anomalous temperature dependence of the solid–liquid interfacial energy can emerge generically in low-solubility systems, even in the absence of complex many-body metallic bonding. This observation highlights low solubility as a key controlling factor rather than a system-specific peculiarity.