See reply above. Did it ever happen to you to come home and find a random fridge in the living room? Then why would you expect that anyone building a secure network would allow anything to be connected to it without any controls?

A smart light bulb usually needs some additional "infrastructure": the bridge that has to be connected somehow. Even if you made the mistake of not physically securing the ports of your secure network, and also don't authenticate any device that connects, and you somehow allow random devices to be connected to a secure [0] network, you'll still be able to catch any device that gets connected. And if your bulb somehow goes straight to WiFi why would you allow random devices on that network?

[0] Did I mention secure enough times? I just have the feeling that this is the crux of the discussion because you consider setting up firewalls and IDS that block any exfiltration as normal but somehow a smartbulb on the network doesn't raise any flags.