Is it obvious? Those existing APIs have known performance characteristics and deep integration into several other libraries. The moment you custom-roll your own root library, you break integration with all existing other libraries that depend on the defaults. To add, your LLM has to think about your new custom version rather than looking at the billions of lines of examples using the one it already knows works from decades of historical data.

If you really, really need some ultra-micro-optimization, you’re obviously not the target of this; but unless you’re doing HFT or the most inner loop of a game engine, the standard library and all its deep integration and battle-testedness is worth the 1% perf hit.