The circle of knowledge in the world they're in would be too small to explain more. It's not like as if those other states will be usable in the moment. The basic 3 will more than suffice for the purposes of his explanation of changing a gaseous state of oxygen to liquid. Also we're talking...
I have a feeling this is series is losing popularity in Japan and the reason the story is taking so many strange turns is the mangaka is being told that it might get cancelled. The mangaka's adjusting so the ending doesn't suffer too badly if it does get axed, but those strange turns are...