Don't know why this is downvoted - it's crystal clear advice for beginners - "just use Django".
You can take care of a lot with just that.
That's the downside of Flask.
And most of the "concepts" Django brings with it are extremely important for any non-trivial web application.
Django also makes it harder to mishandle security.
There seem to be some people who just have a problem with Django choosing sensible defaults for average scale projects.