why was the capital of pakistan shifted from karachi to islamabad?

Wikipedia says:
Traditionally, development in Pakistan was focused on the colonial center of Karachi, and President Ayub Khan wanted it equally distributed. Moreover, Karachi having tropical weather conditions, was located at one end of the country, making it vulnerable to attacks from the Arabian Sea. Pakistan needed a capital that was easily accessible from all parts of the country. Karachi, a business center, was also considered unsuitable partly because of intervention of business interests in government affairs. The newly selected location of Islamabad was closer to the army headquarters in Rawalpindi and the disputed territory of Kashmir in the north.

due to security reason in Islamabad border not meat to any other countries but Karachi sea is the chalenge of pakistan