As someone who had been through both the ward and an outpatient psychiatric facility in my country, as well as a little research, I state openly I am neither a psychologist not psychiatrist. I believe it is a combination of a few factors. Firstly mental health services and care in general has been largely the place to send the problematic or unstable people in your family's to be shut away, up until as recently as the last century, before any kind of psychiatric medication was really mainstreamally used nor effective whatsoever so it carries a historical "something wrong with you, be sent away" stigma. This then bleeds onto the early days of psychiatricy where things like insulin fits, lobotomies and electro shock therapy where commonplace, in the same type of facilities, rendering the placement in one of these facilities for yourself almost a guaranteed zombification if you where ever even deemed fit to leave. In modern terms the use of anti depressants and anti psychotic medication has made the stay in a ward much less timely for most patient's but (though out patient services are offered in my country) upon release very little help is available in most cases post the stay, leaving those vulnerable with little recourse but to continue to take those medications with very little follow up as it is expensive and not always easily nor readily available. Finally it is not only socially unacceptable to talk about these things, as it is both embarrassing for most due to the nature of an "unseen" illness, it is also not something that anyone would look upon as pleasant conversation, especially for those of middle eastern or other ethnic backgrounds due to a cultural bias against things of this nature. In conclusion, centuries of being put away with little chance of release to the modern age of heavily mind altering drugs and little follow up available, has made it ingrained in society that mental health issues, be they severe or not are not things to be openly discussed nor to be proud of speaking up about, leading to the culture of suppression of feeling able to freely speak about thing's of this nature.