1. It silos front end development in Python world. It might be great if your entire team are and always will be Python devs, but what happens when you want dedicated from end developers? What happens when you need to deviate out of what the framework gives you in a front-end context? What happens when you need to eject from "python" into a dedicated front end environment? All your front end code is now written in Python. Worst, you now might even have JavaScript code embedded inside Python code. I keep hearing "CoffeeScript" in the back of my mind...
2. Any python project using FastAPI (which is fantastic), flask, etc. and is growing in scope, will ultimately build Django. For example, FastAPI (which is great), has SqlModel (which is awesome) which makes SqlAlchemy less sucky and more like Django. Start to factor in all the other batteries we got used to getting with Django, and it starts adding up. If the project is smallish in scope and well defined to know it will stay such, sure it's a valid and excellent choice. The same applies here - unless batteries are included, or this is (as suggested in a comment) available as a Django app, you'll end up building Django.