Probably because it's pretty new. React Native needs to start a JavaScript runtime before it can evaluate its JavaScript code, which is what the application log

Probably because it's pretty new. React Native needs to start a JavaScript runtime before it can evaluate its JavaScript code, which is what the application logic is written in, and JS engines are typically not designed to prioritize time-to-interactive metrics and disk usage. Hermes is meant to address some of those concerns and this is probably the next step towards improving those metrics.