Lower Your Rates: On Claims of a Binary Black Hole Merger-Rate Crisis

Recent studies have argued that isolated binary evolution simulations generically overestimate the observed local binary black hole (BBH) merger rate, even after adopting observationally motivated variations in the metallicity-dependent cosmic star-formation history, and have interpreted this as motivation for drastic revisions to binary stellar evolution models. We revisit these claims using a compilation of 1490 simulated BBH merger rates from 57 isolated binary-evolution studies, compared to constraints from the LIGO--Virgo--KAGRA Collaboration through GWTC-5. While about 80% of compiled submodels find rates above the GWTC-5 interval, a substantial subset reproduces or underestimates the observed rate. The literature spans several orders of magnitude, reflecting strong sensitivity to assumptions about natal kicks, common-envelope evolution, mass transfer, angular-momentum loss, remnant formation, stellar winds, initial conditions, and star-formation history. Using 2543 pairwise BBH submodel variations constructed to isolate single physical assumptions, we identify which choices most strongly impact the simulated BBH merger rate. Low BBH merger rates are not uniquely associated with strong natal kicks or reduced low-metallicity star formation. Multiple physically motivated assumptions can independently reduce simulated rates to values consistent with observations. We further show that simulated rates cluster into `simulation silos': frameworks producing apparent consensus within a code that does not generalize beyond it. Our results indicate that claims of a universal BBH merger-rate crisis are strongly model dependent, and underscore the importance of exploring the full parameter space across multiple population-synthesis frameworks before concluding that isolated binary evolution is in tension with gravitational-wave observations.