It is a good question, isn’t it. A young relative asked me, so I cannot take the credit.
Fire is like a flower. It blooms, then dies. As freedumb said, it is magic. :)
Indeed...I emailed an old high school friend who is a Harvard physicist and he said what some posters have said: there is a build-up of gasses just before ignition which causes the big flamer; it then settles down to a stable amount of combustibles.