This is sort of contradictory but at the same time as expected speed up on "realistic" code isn't as big it's also easier for JIT compiling VMs to optimize high level abstractions than something like C.

JIT compilers have different optimizations available like:

Fast inlined heap allocation (normally much faster than malloc/free). V8 even does allocation combining

Transparent ropes for strings

High level alias analysis for hash tables and objects

Inlining dynamic dispatched functions and dynamically loaded functions