Good question. I don't think they care, they're just attempting to validate their own existence.
The thing about Pakistan is that it has a massive identity crisis. They've always defined themselves with respect to India .. there is no standalone identity, they have yet to build the self-confidence for that. They see themselves as a prodigal child of India, a homeland for historical India's muslims - an idea which gets shattered when they realise India has more muslims than them. Keeping this is mind, they constantly need to check on how India is doing to see if their if they're islamic project was worth it, has any merit to it.
Hence why a lot of theads on India's muslims floating around here and the regular chants on 'Thank you Jinnah..
Now, add to that the pernicious effect of their Fauj stoking these religious flames (Kashmir) for their own benefit and welfare, the result is a country with massive identity crisis but also their poor minorities on the receiving end of prejudice.
As for as why Pakistanis care, well 80% of Pakistanis live in Punjab and Sindh, and that's part of historical North India, so we have not only religion, but culture which is similar to them, and therefore we would sympathize with them much more than we would with Muslims from China, Syria, Yemen, Darfur, etc.
Im not saying its right to have more sympathy for one group then another, but thats just how they feel.
And India might have more Muslims, but they don't have political power. And you see that Pakistanis and maybe by extension some Indian Muslims have an identity crisis, because there some aspects of there culture which are different than Hindus, and these cultural aspects originated outside of the subcontinent, so you think they are confused.
I will give you an example of Uttar Pardesh, since my family came from there during partition.
Imagine if Muslims of UP were 80 % of population instead of 20%.
Do you think the official language would be Urdu in Nastaliq, or Hindi in Devnagri?
Do you think Allahabad would have been renamed to Prayagraj?
Do you think Babri Masjid would have been destroyed?
Do you think Mughals, and other Muslim empires would have been villainized as they are today or would they there era would be viewed as a golden age?
Would the the symbols of the state reflect the pre Islamic Heritage of UP or would it be of the Muslim Heritage of UP?
Just some thoughts to ponder.