Many of those high ranking members of Three Great Tribes know about the prophecy of the Ages and they also know that the Conqueror will not came from the Tribes.
How could they accept such things? Accept an Outsider?
To have to worship a man not of their blood! Not of their lineage! So, they wanted to steal His destiny.
Pull the sword from the white stone and take the Conqueror place in history. Anything is better than worshipping and obeying an Outlander.
The Three Great Tribes hated Outlander more than most tribes.
Considering they got the curse for wounding and plotting against Nasrana, killing the Great Prophet most loved person, the bright and fair Red Hair Maiden in his quest of spreading the Truth, no wonder the Three Great Tribes hated Outlanders to their bones.
The Bright and Fair Red Hair Maiden. This is her titles in the obscure books about the first love of the Great prophet.