Isobars are mostly curved and the distance between them is rarely even. This prevents geostrophic winds from developing.
However, wind can still blow parallel to isobars. Besides the pressure gradient force and Coriolis force another force is needed for a balance. The centrifugal force balances these forces by pushing away from a high/low pressure center.
Low pressure system
Around a low pressure center, where the pressure gradient force moves to the center, the centrifugal force helps the Coriolis force balancing the pressure gradient force. Now that all the forces are in balance, the gradient wind moves along the isobars.
High pressure system
In a high pressure system everything goes vice versa. The pressure gradient force wants to go away from the center and the (strong) coriolis force pulls to the center. The centrifugal force pulls away from the center, balancing the forces and in order to create a wind blowing parallel to the isobars.
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