Comment by IainIreland

One major benefit of compiling to bytecode first is that bytecode is a more convenient shared source of truth.

For example, SpiderMonkey has two interpreter and two compiler tiers. The output of the parser is bytecode. We can interpret it immediately, and it's a convenient input to the compilers. It also simplifies transitions between tiers: for example, when we bail out of Warp, we resume at a specific bytecode offset in the baseline interpreter.

I'm not sure how you would resume at a particular point in the execution of an AST-based interpreter without agreeing on a linearized traversal of the AST, which is 90% of the way to bytecode.