[tjalfi]

The proposal[0] gives a rationale. Using builtin functions lets them be variadic without allocating a slice.

[0] https://github.com/golang/go/issues/59488

[morelisp]

While I suspect open coding may make the optimization a little easier, there's no reason it couldn't optimize out a slice and fixed 2-3 iteration loop with the same result.

The proposal's real conclusion was "the decision cannot be resolved by empirical data or technical arguments."