Qi was energy, and it was capable of hundreds of different things, but before it could be able to do all those things, it obviously needed to be talked, to be mastered. A cultivator had to establish their dominance and control over the energy that permeated their bodies and the universe.
For mastery over the elements to be absolute, in preparation for higher realms of cultivation one had to be able to get their Qi to interact with Physical shapes, or to be more precise, the their Qi had to take on a physical form. As soon as Divyat was able to manifest the third element, he strain on him got too much, if all three were manifested as just simple formless yet visible wisps or strips of qi, then he could handle the pressure on his head.
