but a microcontroller with WiFi like the ESP8266 or ESP32-C3 costs less than an accurate hygrometer chip
Ok, two things.
First, the cost of the Wi-Fi chip is clearly not the issue here. The real expense/concern is the effort and software mechanisms needed to secure that network connection. Connecting to the Internet is easy, securing that connected device is hard.
Secondly, at some point you still need the hygrometer, there's no way around that. Either your dehumidifier is tracking humidity, or your home automation system needs to track humidity. And you can't like... get that data from the web somehow, you need a local sensor, and it will generally only make sense to have it in the same room as the dehumidifier (meaning not necessarily where other smart home components are set up).
Well it's a **de-**humidifier. You need to lug water from it. For the dehumidifier in my basement, we have it hooked up to a hose that takes the water right down the drain.
But I do take your point, it is pretty funny.