Gravity Break Historic Background: Coronium is an incredibly sturdy material that was also very cheap to produce during the heyday of the pre-cataclysmic gravitech-based economy.
Though it was near indestructible and cheap to produce, it also was considered deeply unpleasant in smell and texture, as well as being slightly toxic. As such it was mostly used for cheap housing, or for AI-run facilities at a comfortable distance from people.
During the Cataclysm’s early years, coronium became more widely used. There was a need to construct structures that could withstand sudden shifts in gravity, or flying debris. But that was only until the shields were developed. After that, coronium-enhanced properties were once again turned into low-price housing. And new coronium became much more expensive to produce when most of the gravity plants were lost.
But for something like gates and walls, of course an almost indestructible material is still ideal. So Charon assumes that ne will need a lot of power to break through.