Because ctrl-z will stop the current command, and when you run "fg" it resumes that one process. However, the loop you were in has been abandoned, and it will not continue to execute.

For example, try it with this:

    for N in $(seq 10); do echo $N; sleep 1; echo $N; done

You'll see something like this:

    $ for N in $(seq 10); do echo $N; sleep 1; echo $N; done
    1
    1
    2
    ^Z
    [1]+  Stopped                 sleep 1
    $ fg
    sleep 1
    $