I know for the fact that India cannot be indefinitely united by a Single kingdom forever, what I am saying is that Mauryans are able unite South Asia for long enough, there is a pan Indian culture and identity formed, as such when they are formed, all Kingdoms think of themselves as successors of the Mauryan nad try to Conquer all of South Asia
They did to a degree though. Prior to the Magadhi unification, the Aryan states were divided and disunited in all but similar origins in the Vedic Age. Once the Magadhi state unfiied much of the Gangetic Plain, a series of ebbing and flowing Magadhi empires arose. Each of which uniting much of the subcontinent before falling. This lasted for quite soem time, until the subcontinent became more overtly dominated by the Islamic states originating in the north.
And generally, we may say that Hindu geopolitics for most of its history worked as follows:
1. Divided Aryan states in the Gangetic Plains alongside Aryan pastoral peoples of the Indus.
2. Aryan states unite under the conquering Magadhi state of Pataliputra.
3. Magadhi state forms a hegemony over the region, but declines.
4. External western power intercedes in the subcontinent
5. Power bloc arises in the Deccan that resists both powers to its north.
As such, we get a situation of a three way competition that repeats itself numerous times in Hindu history. A competition between an external ultra-Hindu force, a Gangetic state of the Aryans and then a southern based power that opposes the other two. This situation was the famed situation prior to Islam, and provides a great context to the reasons for why unification is difficult.
The iconic example was the fall of the Mauryan empire led to the formation of three distinct blocs. The Shungas, the spiritual successors of the Maurya, the Satahavana kingdom of the Deccan and the Indian kingdom of the Greeks within the Indus Valley. These three fought vigorously with one another, with the Indian kingdom of the Greeks gaining seemingly the advantage over the Shunga during the reign of Meander, with the king forcing possibly the Shunga, the Kosala and so forth under vassalage. Neverthless, the subcontinent could not be united, as the Satahavana stood in the way as a giant guardsman to southern expansionism and a check upon hegemonies in the north. Likely, the Indian kingdom was pressed from the south by the Satahavana and then invaded by the varied Scythian royal elites, destroying the Greek hegemony. Afterward, the Scythian states squabbled and were absorbed into the Kushan empire, which united the majority of the subcontinent in a series of satrapies and tributaries, aside for the Satahavana.
The Kushan came near the destruction of their Deccan rival, but were ultimately unable to finish and were invaded and weakened by the Sassanid state. Thus, developed a return to a three-way conflict in the subcontinent. The Neo-Kushans and their Scythian satraps in the northwest and west, the Gupta in Magadhi and the Satahavana. The Gupta would ultimately gain hegemony, but at a great cost and failed to sustain their victories as regionalism in the south emerged and the turbulence of the northwest sapped their military power.
Finding a way to stop this is difficult frankly. I would suggest, as I have elsewhere, the Kushan empire had the best chance of perpetually uniting the subcontinent before the advent of Islam. As it was lessening western threats while also subduing rebellion in the Gangetic Plains. Its only threat was the Satahavana and the unexpected Eranshahr resurgence in 226-232 CE.