The term "mental health" is such a broad term, for literally thousands of problems, some people have stress, some have autism, some have OCD, some are batshit crazy, that's why there's a stigma to it, labelling someone with mild mental health problems as having mental health problems usually makes people think "they're crazy, avoid".
There were adverts not long ago about talking openly about it and talking to the sufferers about it, shame they took it off the air.