The hatsu not only catches jump attempts, but it also puts you in rekka follow-up state.
The purpose of this, is that the follow-up versions of chun are actually faster than the regular versions, with the air version of follow-up chun being 21 frames, and the grounded version at 23f. Same speed as 6A/3C, while catching jumpouts better.
The hatsu input itself also allows you to option select against rolls. As LK explained, since the hatsu input ends in a 6, inputting it with A+B will automatically barrier should they roll behind you, taking the reaction element out of the initial stages of the tech punish (you still have to remember to dash and 3C)