Because they believed not in God, and trusted not in his salvation:
Genesis 36:37
And Samlah died, and Saul of Rehoboth by the river reigned in his stead.
Psalms 104:7
At thy rebuke they fled; at the voice of thy thunder they hasted away.
Numbers 33:26
And they removed from Makheloth, and encamped at Tahath.
1 Chronicles 1:24
Shem, Arphaxad, Shelah,
Joshua 18:27
And Rekem, and Irpeel, and Taralah,