We are following the Prophet Muhammad who never did Sajda on carpet and always performed Sajda on the earth or plants which are not for wearing nor for eating. All Muslim scholars have the Prophetic Hadeeth: جُعِلت لي الارض مسجدا وطَهورا "The earth was ordained for me as a place of prostration and a material of purification" Saheeh al-Bukhari, Kitab al-Salah, Hadeeth number 429.
The Prophet (SAWA) used to prostrate either on the earth or on piece of clay or mat called Khumrah ( Saheeh al-Bukhari , Kitab al-Salah, Hadeeth number 368) which is just like the Sajdagah which we, Shia Muslims use.
Those who do Sajda on the carpet are doing something which was never done by the Prophet Muhammad (SAWA) according to their own books of Hadeeth. They should ask themselves; why?
Ibn Taymiyyah, the godfather of Wahhabism stated that prostrating on carpet is Bid'ah.(Majmoo' al-Fataawa,Ibn Taymiyyah, Volume 22).