Could you please tell me why the imam during the Zuhr and ‘Asr prayers remains silent and does not recite the Qur’ānic verses aloud as in other prayers? There must be a reason for it. I would like to know it.

No explanation of this exists in the sources. It seems that, in a natural setting, since these two times of the day are bustling with noise and public activity, silent prayers have been preferred. One generally enjoys listening to auditions when silence prevails. One would seldom wish to hear the Qur’ān being read in noisy settings.

This explanation is of course a personal opinion and some other person may offer a better explanation