Why is it slower than native BigInt?

Some benchmarks like the one at https://peterolson.github.io/BigInteger.js/benchmark/#:~:text=Multiplication:%20400%20digits
shows that the native BigInt is 10 times faster.
This is very interesting why... because modern js engines are very good.
Is it possible to have the same speed with js library?

Start by reproducing the linked BigInteger.js multiplication benchmark with JSBI and native BigInt, then inspect the JSBI implementation for the operations measured. Compare results across the benchmark cases and document whether a practical speed improvement is possible; completion would require benchmark evidence and a clearly scoped optimization target.

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