(Upper left) M _mol vs. M _⋆ for PHANGS galaxies (salmon dots; Leroy et al. 2021), M31 (green filled circle; Nieten et al. 2006), and the G2 (red points) and G3 (blue points) simulated galaxies at different times in their evolution. Note that the G2 and G3 simulated galaxies lie significantly below the star-forming main sequence defined by the xCOLDGASS sample. (Upper right) f _mol vs. M _⋆ for the same galaxies. The molecular gas fractions of G2 and G3 are significantly lower than most of the PHANGS spiral galaxies. (Lower left) total gas vs. M _⋆. (Lower right) total gas fraction vs. M _⋆. These comparisons suggest that the low Σ_mol measured for the simulated galaxies might be due to the low total and molecular gas fraction in the initial setup.