Strange in Go start groutine in loop with cancel context

my situation: processor have three retry, and spend second peer retry, and processor cannot be timeout, so i use the CancelContext to controll it.

my processor function:

func process(ctx context.Context, ch chan<- int) {
    fmt.Println("process execute")
    select {
    case <-ctx.Done():
        fmt.Println("process receive done signal, return")
        return
    default:
        fmt.Println("execute default")
        time.Sleep(4 * time.Second) // something handle...
        ch <- 1
        return
    }
}

situation 1

func main(){
    ctx, cancel := context.WithCancel(context.Background()) // handle timeout

    for i := 0; i < 3; i++ { // retry 3
        flag := make(chan int, 1)
        go process(ctx, flag)
        select {
        case <-flag:
            fmt.Println("main receive task done")
        case <-time.After(time.Second * 3):
            cancel()
            fmt.Println("main receive timeout ")
        }
    }
}

output:

process execute
execute default
main receive timeout 
process execute
process receive done signal, return
main receive timeout 
process execute
process receive done signal, return
main receive timeout

question: somethine strange happend, why execute default only print in first loop?

situation 2 i define context in loop:

func main(){
    for i := 0; i < 3; i++ {
        ctx, cancel := context.WithCancel(context.Background()) // define in loop

        flag := make(chan int, 1)
        go process(ctx, flag)
        select {
        case <-flag:
            fmt.Println("main receive task done")
        case <-time.After(time.Second * 3):
            cancel()
            fmt.Println("main receive timeout ")
        }
    }
}

output:

process execute
execute default
main receive timeout 
process execute
execute default
main receive timeout 
process execute
execute default
main receive timeout 

question: why process function never print process receive done signal, return, does it not receive the ctx.Done() singal ?

sorry for my bad english, thank you very much