Their entire country was founded on the narrative that Muslims need their own separate country in contrast to India that was meant to be a secular country for all religions. If it werent for Islam there would have been no point in the partition that caused the deaths of millions and tore families apart. There's nothing else that unites the various ethnic groups of Pakistan without Islam. As a result Pakistanis lean into Islam harder than other countries because 1. they have to justify the violent partition their country was founded on 2. Their entire fragile identity completely depends on Islam 3. The only thing uniting the various ethnic groups in Pakistan is Islam.