为什么通过可变参数的速度如此之慢？

问：

package main

import (
    "fmt"
    "time"
)

func main() {

    n := 1024
    dst1 := make([]byte, n)
    dst2 := make([]byte, 0, n)
    dst3 := make([]byte, 0, n)

    start := time.Now()
    for i := 0; i < n; i++ {
        dst1[i] = byte(i)
    }
    fmt.Println(uint64(time.Since(start).Microseconds()))

    start = time.Now()
    for i := 0; i < n; i++ {
        dst2 = append(dst2, dst1[i])
    }
    fmt.Println(uint64(time.Since(start).Microseconds()))

    start = time.Now()
    for i := 0; i < n; i++ {
        dst3 = append(dst3, dst1...)
    }
    fmt.Println(uint64(time.Since(start).Microseconds()))
}

基准测试结果：

2
2  
2711

为什么通过可变参数的速度如此之慢？