Because that period is dominated by Southern, Western and Eastern Indian dynasties .
Harshwardhana of kannauj the king who was never defeated in a war out of 599 Battles he was involved in ,was Defeated by Immadi Pulekeshi a kannadiga king of Chalukyas . Kannada inscription of 650ad states Harsha lost his Harsha (smile) after being defeated by Pulekeshi2.
The Naramada river became the Border between these 2 Powerful Kingdom between 6th to 8th century .
Harshawardhana was later given the title Utterapateshwara (Ruler of the North) , Pulekeshi was given the Title Dakshinapateshwara(Ruler of the South) .
Later Rashtrakutas , Gujratha pratiharas and Palas , A kannadiga, Gujerathi/sindhi and Bengali dynasty were in tripathit struggle for the domination of Central India between 8th century to 10th century .
From 10th to 13th century chalukyas of Karnataka made a comeback and were at logger heads against Eastern Gangas of Odissah and Cholas of Tamil Nadu
So because of Weak politics of Karnataka , Gujerath , MP, odissah and Bengal we are not able to bring this part of History to Indian History Books .