Theory:

Vijayalaya line of Chola rule decline after the death of Rajendra Chola, as his successors were incapable. After Athirajendra, Eastern Chalukya ruler Rajendra Chalukya seized the Chola empire and began the rule of the Chalukya-Chola dynasty as Kulothunga I.
 
Rajendra_Chola_I_-_Chola_State.jpg
A painting of Emperor Rajendra Chola I.
  
Kulothunga lost the Chola territories in Ceylon, and the Pandya territory slipped out of Chola control. Kanchipuram was lost to the Telugu Cholas. In AD 1279, King Maravarman Kulasekara Pandyan I defeated the last king Rajendra Chola III and established the rule of the Pandyas in present-day Tamil Nadu.
 
Kulothunga_territories_cl.png
Map showing the extent of the Chola empire
during Kulothunga Chola I.
Reference:
Image source:
1. https://commons.wikimedia.org/wiki/File:Rajendra_Chola_I_-_Chola_State.jpg
2. https://commons.wikimedia.org/wiki/File:Kulothunga_territories_cl.png