Suggestion to have deleting projects delete both unassigned and assigned tasks unique to the project.
If you also wish to delete assigned tasks you can for example use the multi-select in list view to unassign them first.
I second this one (and I know others would as I have seen other forum posts about it). It seems odd to have tasks still assigned when a project is deleted. It is way too manual of an ask for us to go and remove assignees before deleting a project.