[ptx]

The JVM version implements a JIT compiler; the C version implements an interpreter. So it's the same thing that makes PyPy faster than CPython, Java 1.3 faster than 1.2 and the first release of Chrome's V8 faster than earlier JavaScript implementations.

PHP 8 also introduces a JIT compiler, which is presumably less mature but more complete: https://wiki.php.net/rfc/jit

[pilif]

also, the implementation we're talking about is not a complete implementation of the PHP language.

It's easy being faster when you're doing less.