Having N sources of dry air (the vents) and one or two sources of humidity, scattered over your house, coming in and off all the time is a lot let desirable than a static system linked to your opening and closing of doors plus house leaks. It’s difficult to tune.

Sure, less desirable, but you you can buy n humidifiers

That is the simplest method. I grew up with a hot-air wood furnace in the basement, and we just stuck a giant galvanized pan on top at the start of the ducting. About once a week I'd have to fill it back up.

Man, I miss wood heat.