Ahmad Abubakr 11 November 2019
The simple answer is that they did not want to. Nor were they given such options.
Sindh
Sindh’s accession to Pakistan is simpler. At the time of partition, Sindh was a Muslim majority region by 75%. Sindh was also the province that was most loyal to Jinnah and the idea of Pakistan. In the 1946 elections, the Muslim League won 82% of the Muslim seats. At the time of partition, the Sindh Assembly chose to become a part of Pakistan.
Balochistan
Balochistan’s case is a bit more complicated. Prior to the partition, Balochistan was not as it is nowadays. It was not a unified province. Instead it was made up of Chief Commissioner’s province and four princely states. The princely states being Kalat, Makran, Las Bela and Kharan. Las Bela and Kharan were kind of vassals to Kalat.
In 1947 at the time of partition the Chief Commisioner’s province became part of Pakistan. Furthermore the princely states of Makran, Las Bela and Kharan acceded to Pakistan. The only princely state that did not was Kalat. This is a very common misconception. Almost all of Balochistan immediately joined Pakistan by choice.
Ahmad Yar Khan, the Khan of Kalat, instead wanted Kalat to be independent or atleast semi-independent. At this point Pakistan had not officially accepted the accession of any of the Balochistan princely states. Historically, Kalat had leased territories that were now part of the Chief Commissioner’s province which had joined Pakistan. The Khan of Kalat wanted these returned to Kalat. He was told by the British that as Kalat was a part of India and not an independent region, he must choose between India and Pakistan. This presented him with a problem. He either had to accept that Kalat was an Indian state and could regain the leased territories but join either Pakistan or India. Or he could declare Kalat as a non-Indian region and be independent but lose the leased territories. Ahmad Yar Khan wanted the positives of both which neither Pakistan, nor the British were willing to do.
After almost a year of talks with nothing achieve, the other princely states were losing patience. Las Bela and Kharan wanted to join Pakistan as independent states separate from the rule of Kalat. They informed Pakistan that either Pakistan accepts them as separate states from Kalat now or they must start making preparations to defend themselves from the Khanate of Kalat. Pakistan at this point accepts their accession on 17 March 1948.
Nawab Bai Khan Gichki of Makran accedes to Pakistan as well soon after. This leaves Kalat in an impossible situation. It is now landlocked and surrounded on all sides by Pakistan. He now had little choice. He had lost all his vassals to Pakistan and the coastal route (Makran) was cut off as well. After a series of negotiations Ahmad Yar Khan signed the instrument of accession. His brother, Prince Abdul Karim, rebelled against the decision. This would be the start of the insurgency in Balochistan.
The flag of Khanate of Kalat
Summary
Sindh was a Muslim majority region that voted to be a part of Pakistan. It had no intention of being independent, nor was it given the choice by the British.
Balochistan’s Chief Commissioner’s province immediately joined Pakistan. The princely states of Makran, Kharan and Las Bela all wanted to join Pakistan. Las Bela and Kharan were vassals of Kalat and Kalat wanted them to remain so. Las Bela and Kharan both made it clear that either they would accede to Pakistan separate from Kalat or they would fight to defend themselves from Kalat independently. Pakistan accepted the three princely states and Kalat was left landlocked. Kalat accedes to Pakistan on 27 March 1948.