Because it may not have caused a massive energy spike. If anything, it’s more likely that the orichalcum, animal-people and monster’s creation mitigated the energy spikes from the release of the four elements from their bindings, which, in turn, already had Earth on a higher energy level than standard.

Basically, it can be argued that one of the Law of Conservation of Energy is in play here, even if we’re paying attention to Magical Energy. Before, all the magical energy was an Element’s Potential Energy, or was being used to ensure that the Elements were sealed. Releasing the Elements allowed the Potential Energy to be released and produced Monsters, Animal People and gave people access to magic, sure. But all of the previously Active Energy that was being used to seal them transitioned into more potential forms, making magical minerals such as orichalcum valuable again.

All in all, releasing the Elements allowed the previously Potential Elemental Energies transition into Active Elemental Energies, while the Active Sealing Energies transitioned into Passive Mineral Energies. It would be more akin to having a pair of lights setup on a singular switch so that one is always on and one is always off. Flipping the switch changes which light is on, but the amount of constant energy stays relatively the same, though there would be a rapid blip of energy at the point of transition that is effectively over in a hundredth of a second (assuming it does work the same way as the light-bulb in the analogy).

Then Shidon took those Passive Mineral Energies and slowly worked out how to use them for things. While this would result in a gradual increase in Active Energy, it’s gradual instead of rapid, and if they look they’ll just see that Magic has been reintroduced to Earth, so that’s expected as people learn or develop their ability to tap into the energy anyway. Doesn’t seem to me like there’s any reason to look at Shiden’s factories from that.

The only reason Yuki is looking at the Android Girls so closely is because she’s not a innately born Celestial, because she knows that they’re being made from nothing, and because Phil is here and finding out the secrets behind the Null is important to every race that is inherently made of magical energy.