No Pakistani prime minister has ever served a full term in government.
What are the exact flaws in Pakistan's parliament that prevent their prime ministers from staying in power for an entire term?
Many democracies have a vote of no confidence, but not all. For instance, the US only allows an impeachment for cause, not simply for a lack of confidence. This is one of the differences between presidential and parliamentary systems.
Some systems have only constructive votes of no confidence, requiring the opposition to unite behind an alternative, not just in their dislike of the incumbent. Such a rule would reduce the number of no confidence votes.