Why subcommand help doesn't work when i give an argument without --

Python Help
1

here is my argument parser code

import argparse
from argparse import ArgumentParser
def parse_args() -> argparse.Namespace:
    parser = ArgumentParser(prog="t3 res", description="Request or manage lab pool resources.")

    parser.add_argument(
        "--json-output-file", help="Write the json output to the specified file."
    )
    parser.add_argument("target", metavar="TARGET", help="IP/Hostname of a RPi attenuator or Sector name")


    subparsers = parser.add_subparsers(title="sub-command", dest="sub_command")
    ramp_atten_parser = subparsers.add_parser("ramp_atten", help="ramp to given attenuation")
    ramp_atten_parser.add_argument("channel", choices=["H", "V", "HV"], help="which channel(s) to set")
    ramp_atten_parser.add_argument(
        "-t", "--interval", type=float, default=0.5, help="the interval between each step in seconds"
    )
    unreserve = subparsers.add_parser("un", help="Unreserve pool resource(s).")
    unreserve.add_argument("id", help="Resource pool ID (typically given by t3 res res).")


    return parser.parse_args()

args = parse_args()


▶ python3 tr.py ramp_atten -h
usage: t3 res [-h] [--json-output-file JSON_OUTPUT_FILE]
              TARGET {ramp_atten,un} ...

Request or manage lab pool resources.

positional arguments:
  TARGET                IP/Hostname of a RPi attenuator or Sector name

options:
  -h, --help            show this help message and exit
  --json-output-file JSON_OUTPUT_FILE
                        Write the json output to the specified file.

sub-command:
  {ramp_atten,un}
    ramp_atten          ramp to given attenuation
    un                  Unreserve pool resource(s).

but if i use --target instead of target it works

▶ python3 tr.py ramp_atten -h
usage: t3 res ramp_atten [-h] [-t INTERVAL] {H,V,HV}

positional arguments:
  {H,V,HV}              which channel(s) to set

options:
  -h, --help            show this help message and exit
  -t INTERVAL, --interval INTERVAL
                        the interval between each step in seconds