@Noscoper
Gangetic Valley was under almost 500+ years of continuous Muslim rule. The center of Indo-Islamic civilization was in Haryana, UP and Bihar.
Indus valley(Sindh, Punjab and Kashmir Valley) converted to Islam only when the Landed Elites converted to Islam. Sindh began to islamize with the rise of the Soomro dynasty, who were Muslim Rajputs, and the Rajput castes became muslim as a result.
As for Multan, Ismailis control led to repression of Hindu practices and decline of that religion, with Ghaznavid rule accelerating this process.
For Punjab, Lahore was selected as the Ghaznavid capital with Persianate culture being established here, and some Landed elites became muslim. This process accelerated during the Delhi Sultanate under Sultan Balban's rule who organized mass conversions to Islam in Western Punjab especially with groups like the Khokhars.
For Kashmir valley, the Lohara dynasty was the Hindu regime and was highly unstable. The frequent instability of the Kashmiri Hindu state given excessive conflicts with the Damara nobility along with state corruption led to the decline of Hindu religion. As such, the Tibetan adventurer Zulchu overthrew the Loharas, and instead of converting to Hinduism he converted to Islam as the Kashmiri Pandits refused to induct him into the religion. He was succeeded by Shah Mir dynasty who were also immigrants from elsewhere. During this period, Islam rose due to State policy, and Sufism , which resulted in the Damara nobility converting to Islam along with their clientele. The Kashmiri Pandits were not a part of this process and as such they are the only Native Kashmiri Hindus remaining.
For Bangladesh, it was the disproportionate growth of Muslim Peasantry versus Hindu peasantry due to clearance of Delta forests under Mughal rule. The delta was still mangrove forest and still had to be cleared, and Bangladesh east of Gangetic river was less developed and had less entrenched "Hindu culture" . There was also SE Asian groups like Koch and Mech people who were culturally and genetically quite different from the Indo-Aryan West Bengalis- in fact these were probably the first people in Bangladesh who adopted Islam on a very large scale. There's also some religious fluidity due to the fact that religious was previously more Hindu_Buddhist syncretic, FYI just check out the Bauls who were into Tantric culture which encompasses both religions.
For Pashtuns and Baloch, it was the conversion of entire tribes to Islam probably during Saffarid, Samanid, Ghaznavid and Ghurid periods and was a completely separate process from the spread of Subcontinental Islam.
In other words, basically for completely opposite reasons Indus Valley and Bangladesh became Muslim.
To make Haryana/UP/Bihar Muslim you need to make the Landed Elites muslims, and propagate Islam amongst the Peasantry.
Perhaps an Indigenous Muslim dynasty instead of Muslim rulers of foreign extraction would help. A Muslim Rajput/Yadav/Ahir dynasty? Perhaps patronage of sufism could spread it amongst peasantry.
Not sure how effective this will be.It might just lead to an extremely divided society rather an Islamized one.