Neat question;
I think it comes down to how you define the boundaries of ‘chin’. Do you have it naturally, or can you develop it through training? Does it actually come down to the strength of your neck? Perhaps heavy hitters don’t develop the physical fortitude in taking a flush hit to the face because they pick out their single power shots to try and end a match early, don’t train for extended boxing matches?
I think it comes down to how you define the boundaries of ‘chin’. Do you have it naturally, or can you develop it through training? Does it actually come down to the strength of your neck? Perhaps heavy hitters don’t develop the physical fortitude in taking a flush hit to the face because they pick out their single power shots to try and end a match early, don’t train for extended boxing matches?