It is because since the last 5 years, India's military actions are not at all geared towards Pakistan. We know that Pakistan does not have the military capability to finish India's nuclear assets in a first strike. Neither will Pakistan ever have this capability. This is not a boast, simply an assessment based on Pakistan's military resources and our own and the rate at which they are growing.
Ergo any new development - like SSBN's or ICBM's are not meant for Pakistan in any way possible. They are meant solely for the great powers.
The development of an SSBN or lack thereof does not in any conceivable practical way affect Pakistan or its military posture. We always had second strike against Pakistan on the basis of our land and air deployed nukes just like Pakistan has second strike against India.
The brouhaha in Pakistan over India's SSBN is just that...noise. It stems from Pakistan's desire to "match India" rather than any practical assessment of need or target.