Hard water often contains hard to dissolve minerals. An evaporative humidifier over the time accumulates limescale and it’s very difficult to remove it, you cannot just dissolve it. With ultrasound humidifier all this limescale will be in the air. Admittedly not in all regions the water is hard but if it is then ultrasound humidifier will be a bad choice.

Depends whether you want that stuff in kidneys and what have you.

Bigger particles are known to irritate the lungs and even cause asthma (google or ask gpt)