If the sun worked by burning hydrogen, first of all there would have to be a lot of oxygen on the sun, and second of all, it would have burned out long ago (millions or billions of years ago).I don't understand why they don't just convert to burning hydrogen.
It's good enough for the sun.
ICEs can run on hydrogen but that is a major development and research project in its own right. I feel like direct synthesis of hydrocarbon fuels is more promising so we can keep using the engines we already have and know how to make. Also, when storing fuels, it is a lot easier if they are liquids.
Maybe the best thing is to pursue all of these concepts simultaneously. Maybe in the end there will be some mix of solutions that are used. We probably don't know enough to pick the winner now.