Is it necessary for the company to provide reason to the staff if company felt that the staff is not suitable for the position?
It is not necessary for the company to provide reason to the staff if company felt that the staff is not suitable for the position, as long as the necessary payment for the termination is paid rightfully.
However, as a Human Resource practitioners, you should always implement a correct approach and process in the termination of service and performance management. The employee shall have the chance to make known of his / her performance and have opportunity to raise his / her concern to his supervisor.
It is always good we implement to session of probation review, for example, 1 after six weeks of joining and 1 after 12 weeks of joining (if confirmation is 3 months).
This is at least to allow the employee to know about the company expectation and his own perception of the performance.
It is being unfair if the employee is told to leave after 3 months without prior discussion about the performance, well, he may think that he is doing well.