Why do I have to activate my virtual environment for the second time - i.e. from within a Python script despite having it already activated?

Question

I wrote many scripts to help me manage my django projects. One of them, cr_app.py creates a new app:

#!/usr/bin/env python3

from subprocess import run
def main():
  create_app()
   
def create_app():
  name = input("The name of the app?\n")
  run(f"""python3 manage.py startapp {name}""", shell=True)

if __name__ == "__main__":
  main()

When I am inside of my virtual envirnment's project directory, having activated it with . bin/activate, and, following the tutorial, I run manually python3 manage.py startapp polls then I find models.py already created inside of polls/. But this does not happen, models.py does not get created, when I run cr_app.py and create a new app polls even though I run this script while being in the projects activated virtual environment (although cr_app.py is not, it is located in a different, remote directory). The directory app, polls/ gets created but without models.py inside of it. Activating the environment from within the script with run(f""". bin/activate && python3 manage.py startapp {name}""", shell=True) fixes the issue, and models.py gets created. Why do I have to activate my virtual environment for the second time - i.e. from within a script, after having it already activated?