After the Qin dynasty ended the Warring States Period in about 221 BC, historical China(The coastal part, so no Tibet or East Turkmenistan which are modern conquests) was essentially unified and never really broke up again.

In India on the other hand, not only was all unification temporary. (Chandragupta and Asoka pulled it off for a bit and the Moguls kind of managed it for about 200 years, and really only the north for most of that). But religious and cultural differences, especially between the North and the South, were much more stark.