Comment by flohofwoe

Because 64-bit WASM can be quite a bit slower than 32-bit WASM:

https://spidermonkey.dev/blog/2025/01/15/is-memory64-actuall...

TL;DR: wasm64 requires explicit heap bounds checks, while in wasm32 the memory mapping hardware does it for free.

E.g. quote:

"The only reason to use Memory64 is if you actually need more than 4GB of memory.

Memory64 won’t make your code faster or more “modern”. 64-bit pointers in WebAssembly simply allow you to address more memory, at the cost of slower loads and stores."