Thank you for the so detailed comment @glenalbrethsen! (and sorry for replying so late)

Mental health becomes a taboo because of the "stigma" it leaves on the individual and because for lots of people, admitting that you're not ok and you need help leads to an over-generalization that you're insane. Which of course does not apply in all cases. I believe this is a good reason why most people do not seek help and bear the burden on their own...