Tails: Nodes with no dependents.
Someone could implement this as a feature in graphviz. It might take a day to implement.
There are probably other "solutions" that already handle this more gracefully, but otherwise don't have a very complete set of features relative to graphviz.
It's reasonable (and constructive) for you to complain, but your "issue" is representative of a wide set of "issues" we've seen, and the real problem is we're just a little unimportant niche service and all this work is being done by volunteers and they mainly work on the things they know how to do.
So far it has automatic layout that will position (and create a rendering) for hierarchical graphs - even if your data isn't hierarchical in nature. This is how the algorithm works internally as it is a reflection of Dagrejs.
I plan to support more layout types in the future.
As for placement of 'root' nodes (aka source and sink nodes) - in reference to the parent comment - my hope is to expose graph theory methods that you can run before layout/render which would help facilitate this automatically, but it's non-trivial to codify as it requires a substantial refactor to the layout algorithm(s).