Nepalis and Sri Lankans have been anti India and want to show their anti ness by supporting Pakistan many times we have seen in last 10 years. They consider China as the best thing ever and India is the quissential poor hungry country with no toilets.
Long back Indians used to pamper them just like MMS govt and allow all their shit.
Like today's Govt, we don't give shit about them, let them get raped by China many times offline and online and then let them come over. We will use them once they are defeated. This is realpolitik. Let them enjoy their flirts.
The name for this subcontinent through the millennia has been India or Bharat and after British left we named the largest country India.
Within Bharat we have multiple peoples, ethnically, linguistically and religiously different people.
Their nationalism ie desire to make state for Nepalis or Lankans is opposed to ours by default.
Not that it threatens us but that it's a diverging route.
Nepal or Sri lanka joining Indian Union doesn't affect yours or my life in a huge way.
It will be like just another state.
For them it will be like nearly negating all of their nepali or lankan identity built over decades.
For people in India, wearing Multiple identities is not a huge deal.
They also realise this. This they have to compensate by exaggerating their "non India ness" and some anti india attitudes.
Other things that explains anti india attitudes is india's involvement in their domestic affairs.
Just like how we hate US and USSR for meddling in our affairs.
We don't have the tact and soft power to woo their people and culturally influence them.
The only efforts bollywood has made is towards Pakistan like this selmon boi movies.
So it's basically little man syndrome plus lack of good diplomacy and softpower from us.
Some degree of anti india attitudes and desire to establish some separate identity will always be there by default.
(In case of raqibuls and porks, jihad and larping also plays a significant role.)