It's an overkill for the task creation form to link such a rarely used feature as "Create New Project". Task creation is one of the entry points for new/casual users, and it is good to offer them just the fields they will need in order to keep focus an to diminish the risk of confusion. What if we just remove it?
Creating a project is a significant action in your average Phabricator instance, not something done lightly when you are in the middle of a task creation. In addition to this, probably many instances restrict the creation of new projects to a certain group of users, which makes that link even more pointless. This is the case of this instance here, also of Wikimedia's instance, where users clicking that link will only get a dialog like:
You Shall Not Pass: Projects You do not have permission to create new projects. Users with the "Can Create Projects" capability: Members of the project "Meta-Project Creationists" can take this action.
Therefore, if you we are not convinced about removing the link entirely, at least it should be shown only to users with permissions to create projects.
Initial report: https://phabricator.wikimedia.org/T78245