How did sindhi hindus became a majority in urban sindh, while same was not the case in 1200s when sindhi buddhists were majority in urban areas?

By 1947, in major sindh cities like

In Karachi, hindus-sikhs (51-7%) made up upto 60% population

In Sukkur, 70% of the people were hindus

In Hyderabad (sindh), hindus made up 70% of the people

So how did such a big change happened over a period of 750-800 years? How did sindhi hindus grew so much while Sindhis hindus made up only 26% of whole sindhi population?