For the social status quo, we are generally expected to act happy or "fine". When asked the question "How are you," the expected answer is usually fine, good, or okay, even if that answer isn't true. In a social setting where small talk is expected, it does not fit into social norms to talk about deep negative emotions. Expressing anger, sadness, and emotions like them leave surrounding people uncomfortable. The social status quo isn't for our own benefit but for the benefit of others. It is followed not to make ourselves comfortable but to make others feel more comfortable around ourselves. Negative emotions in public settings are looked down on most of the time leading people to either try listening in for gossip or turning their head to ignore it.
However even in general, negative emotions are difficult to deal with leaving people uncomfortable just by feeling them. Some people aren't even taught healthy ways to handle them which makes them even more difficult to be accepted. Despite how uncomfortable these emotions make us or others feel, it is important to exercise them in a healthy manner because when they are not, it results in them becoming bottled up. Bottling up our emotions leads to a negative outcome, small or big. Even if expressing them in public is against the status quo, they can still be handled in a more private setting in a safe place surrounded by trusted and close people because these emotions are difficult to deal with, but they don't have to be handled alone.