By that logic, you will not buy any "smart" devices
A camera doorbell, in your example, need wifi password so that it can stream video.
A smart lightbuld need wifi connection to change brightness or color.
Without wifi connection, it will lose a part of functionality
Giving something wifi password is different from giving something internet access, they are not inclusive. You just add it to your local network without giving it internet access
In your case, does your smart bulb still have same functionality if you dont add it to your zigbee network ?
"MACsec (802.1AE) and EAPOL (802.1X)", https://forum.openwrt.org/t/macsec-802-1ae-with-802-1x-eapol...
There are protocols like zwave, zigbee, and possibly others that not only not need wifi passwords, they don't even need an IP address.
There are plenty of smart devices (including lighbulbs, sensor movements, and what not)t hat use bluetooh, or protocols like Zigbee that enable all kind of functionality without wifi password.