He had once foreseen the destruction of the Otsutsuki clan. They would encounter an interstellar civilization—a civilization on the level of an interstellar hegemon. It was the most powerful civilization their clan had ever encountered, and the first and only one.
It was an extremely powerful civilization that had been developing in the universe for even longer than they had. Unfortunately, it had never discovered how to transform natural energy—a primitive, special power confined to planets—into chakra.
In fact, even the Otsutsuki clan of today had never deeply studied this transcendent power called chakra, nor how to reproduce it without relying on the Divine Tree.
They knew even less about natural energy!
Otherwise, after suffering a setback in the Shinobi World, Ōtsutsuki Isshiki wouldn't have used natural energy to evolve his Kāma. He didn't understand this power. If Ōtsutsuki Isshiki had known about natural energy and understood it, Kāma would have evolved long ago. Would he have needed to wait until then?
There was also Sage Mode—a method of gaining even greater power by mixing natural energy with chakra. To some extent, this transcendent power existed on all the life-bearing planets in the universe.
Unfortunately, every time they planted a Divine Tree, they used it to devour all life on the planet, leaving behind nothing but a dead world. As a result, to this day, the Otsutsuki clan had barely studied natural energy at all.
That was perfectly normal. Natural energy was a decent transcendent power, but by the interstellar age, it had become somewhat outdated!
Without knowledge of chakra, it was very difficult for a civilization to create this transcendent power.
The powerful interstellar civilization the Otsutsuki clan had encountered back then had never mastered chakra, the transcendent power that could let a civilization's people ascend through spiritual energy.