Is the sitting for rest a Sunnah, and why do the Imams of the Haram, such as Sheikh Abdur-Rahman Al-Sudais or Usamah Al-Khayyat, not apply it in their prayers that are televised?

Scholars have differed regarding the sitting for rest (jalsat al-istiraahah). The majority opinion is that it is not a Sunnah, while the Shafi'is, and it is also a narration among the Hanbalis, hold that it is a Sunnah. So perhaps Sheikhs Al-Sudais and Al-Khayyat are among those who believe it is not prescribed by the Sunnah.