JITs exist because 1. certain compilation can't be done at compile time, because the code is dynamically synthesized at runtime from data only available at runtime; and 2. knowing how the code is already being used at runtime through an interpreter, can help optimize the compiled code ("profile-guided JIT.")

Bundling on first request has neither of these advantages: everything that is getting compiled at runtime could have been compiled at compile-time; and no information is yet available on how the code will be used.