Dark Harvest + Demolish = Split Push Nightmare?

So, I decided to pick up Yorick for my late game pusher, and made an obvious discovery trying different runes on him:

Dark Harvest can proc on both Champions and Structures.

And during one game with duo support no adc bot lane (long story) where my team won off the back of Teleport, Ult, and a select few runes and items, I cracked both nexus towers and the nexus itself in less than a minute (mind you super minions were in the base, otherwise tping would have ended badly).

So my question is, "Why does the majority of Yorick, Nasus, or any Split Pushing Farmaholic players not utilize the synergy between Dark Harvest+Demolish more?"