It's a well-known fact that for good or ill, life in the Crystal Empire can only stem from Love. A lot of Love, in fact. Even with the participation of a Love-specialist Alicorn Princess, powering the heart still required the whole general population to pitch in and keep the elements out. It is also known that in Equestria, Love isn't just a concept, not even a driving emotion or temporary insanity; it's a perceivable form of energy made manifest in a wide array of spells and effects. Further, it is known that Fear, the Love-killer, was quite abundant in the Crystal Empire. In fact, there didn't seem to be a single pony lacking in it.

Mathematically speaking, in the time of King Sombra's reign, somepony had to generate enough Love to equal the entire city's output, at least twice. So where was all that Love coming from?