Force Crystal Mines were quite rare existences. Even after all of Leonel's travel, his stints on Planet Valiant and even his robbery on Planet Vincero, Leonel had still yet to run into a second Force Crystal Mine after the one he found on Earth.
What Leonel hadn't known back then was just how rare Force Crystal Mines were. To be produced, they not only needed time, but they also needed a world of a certain talent to produce the Force density that would be required.
Even something like a Force Eruption, which had the function of quickly increasing the energy density of a world, was an absolutely rare event only the most talented of worlds would experience. Other worlds would have to slowly accumulate their Force over time rather than being gifted it.
If one thought about it, didn't it make more sense for the common currency of the Dimensional Verse to be Force Crystals as opposed to Urbe Ore?