vijayanagara was a small kingdom similar to the size of Nizam of Hyderabad or Ranjeet singh , however "the Chola Dynasty" was another Beast altogether , & it was one Kick A$$ Power House encompassing south India , parts of indo-china & Indonesia the empire stretched more then 6000 km with a huge area size of 1.3 million sq mi or 3.6 million sq km ! , it was bigger then present day India , UK , & Switzerland combined ! , however, it was more of a south east Asian power, rather then a south Asian one , there for, it is not mentioned much especially in the context of other kingdoms or empires like the Mughals or Maurya's , which were more of a south Asian powerhouse (India-Pakistan -BD & parts of Afghanistan) secondly when it came to the Chola dynasty, the language & culture were also quite different, as it was not an Indo-Iranian one like Sanskrit or Persian which dominated both kingdoms like Maura or Mughals
etc & with which both formed a very strong rooted cultural identity, that we see in present day India-Pakistan , as for Ahom again it was too small so as to have the type of historical impact that is needed to, The Chola Empire did it however they did it, in the wrong side of the bay of Bengal ! the realms of power & dominance in south Asia lies in India/Pakistan & Afghanistan, it has always been like that , from the Buddhist periods,
to the Hindu kingdoms to the Muslim ones , heck even Mahabharat needed to be there
The Chola Empire