We looked at these when we started. The problem with them is that they weren't designed with constrained resources in mind and it shows. For example, objects are hash tables and method calls are thus expensive. An obligatory top level execution makes startup slow, ...

If you have a bigger machine you can optimize some of this (V8), but these optimizations typically need memory and/or a JIT. (And Python struggles to optimize even on stronger machines).

By starting from scratch (with what we learned from V8 and Dart) you can design something that feels similar but is much cleaner and faster to run.