Why So Many Prophecies of the Khawarij?

Out of all the deviant sects out there, no deviant sect was prophesied by the Prophet (peace be upon him) like when it comes to the Khawarij. We have multiple authentic ahaadith attributed to the Prophet (peace be upon him) where he described the features of the Khawarij.

But why single out this group? Why don't we see the same prophecies and warnings of the Rawafidh, for instance?

Well, three possible reasons are:

1) They were the first organized sect to deviate as a group from the path of orthodoxy in the history of Islam.

2) Their danger is not only ideological but also physical in that their ideology directly results in the shedding of innocent Muslim blood.

3) Their fitnah is exceptionally misleading. The Prophet (peace be upon him) informed us that their prayer and Qur'anic recitation are superior to most of ours and would put our prayers and recitation to shame. Nevertheless, the Prophet still warned that they are deviant. In light of this, more people would likely have fallen victim to their fitnah if they had not read this warning in the ahaadith.

- paraphrased from Shaykh Abdullah al-'Ujayri