Reason Why...

We suppress our emotion because, we don't want to get hurt, the fear of being vulnerable, labelled a cry baby, defense mechanism, societal expectations etc. Therefore, as a result, we forget that concealing our emotions can have some pretty significant effects on physical and emotional health.

Although, this is more common in men than in females, due to the expectations the society has placed on them (A man should be always seen as a tough and hard guy). Forgetting that If they keep hiding their emotions it could get to a stage of being self destructive causing emotional and mental breakdown.