In a parliamentary system the executive is weak because it is

Explanation

A parliamentary system is a system of democratic governance of a state where the executive derives its democratic legitimacy from its ability to command the confidence of the legislature, typically a parliament, and is also held accountable to that parliament. In a parliamentary system, the head of state is usually a person distinct from the head of government. This is in contrast to a presidential system, where the head of state often is also the head of government and, most importantly, the executive does not derive its democratic legitimacy from the legislature.