Dammit, forgot the why part.
With Fate, even though it faithfully sticks to the source material's plot, it is probably the most structurally coherent of the videos I've done, as I made the concerted effort to move through the development in a clear manner. Also because of the difficulty I had in editing, rendering, and encoding it on a computer that by all rights should probably have keeled over 7 years ago.
Eien was a lot more conventionally edited, but I also specifically played the mood, and there's a couple editing and masking tricks I'm still rather proud of myself for.
Like I said before, though, I'd prefer it if the real answer was that I've not actually done anything close to my magnum opus yet. The forced hiatus from editing I'm currently experiencing due to finally having it with hardware limitations is really the only reason I haven't released anything since Eien.