Elucidating the fundamental effects responsible for phase stability and band gap tuning in hybrid perovskites is of critical concern for the further engineering of these promising materials. With recent experimental evidence suggesting increased phase stability in perovskite alloys, the field has labeled entropy stabilization as a likely hypothesis. We clarify the phenomena of entropy stabilization and show, using first-principles density functional theory calculations, that perovskite alloys are not uniquely entropy stabilized by quantifying the site-specific enthalpy and entropy contributions of different cations and anions. We propose that only a small set of these materials are entropy stabilized, and that observed stability effects are primarily enthalpy driven. We also unravel the effect of alloying on three distinct sublattices (A, B and X in perovskite ABX3) on the band gap in perovksite alloys, and provide insights into the general trends of the band gap evolution with chemical composition. Our results show that alloying on the B-sublattice have the strongest effect on the band gap as it influences both the valence band and conduction band of the alloy band structure, and explains the origins of recent experimentally observed large band gap reduction in Pb-Sn based alloys.