What's considered "healthy" and "optimal" by research conducted by and on folks living in the higher and drier northern latitudes doesn't always match what people in the tropics "feel".

The annual average for humidity is 77% where I grew up, and highest humidity is around 88% during the monsoons. Well outside your healthy range. My childhood home doesn't have air conditioning to this day, so I do feel these humidities whenever I'm there. And I like it, unless it's peak summer (I adore the monsoons - it's my favourite season, and I miss that I don't really have "proper" monsoon rains where I live now). Most friends who still live there also adore the monsoon weather - though they hate that their clothes takes days to dry after a wash, and other inconveniences. None of them use dehumidifiers, or complain of humidity outside the summer sweating season.

The annual average where I currently live is 55%. Which is pretty high on your healthy range. But my skin feels dry AF, even with daily moisturization, my lips crack if I drink < 5L water per day, and my hair has this brittle texture I don't like. All of which disappears after a week in my childhood home.

So high humidity might promote mould growth (though I have never encountered it myself, it's entirely possible we will find some if we break the walls down), but to people who grew up with it, it can also feel comfortable. Hence the market for humidifiers, with air conditioning on the rise - rather than dehumidifiers.