Why would a connection to internet need security updates?
At the point the software is released it has (hopefully) no known security vulnerabilities, which is a reasonably secure situation to be in.
However, eventually some of them will become known, and that is not safe.
We, as an industry, are bad about pushing "every device that is on the internet needs to be as up to date as possible all the time" when it reality there is a lot of unimportant stuff on the internet.
It's like locks. I wouldn't secure my house with a bike lock, but it's fine for my bike. My bike is less full of important stuff.
At best, that means you're externalizing the costs, i.e. now your device is part of a botnet and becomes a problem for other people. But of course that assumes that it doesn't become a problem for you as well; a compromised device on your network is a great launching point for local attacks and a way to send illegal traffic out through your internet connection.
I have a couple Raspberry Pi Zeroes that monitor aquarium temperature. I keep them updated.
Meanwhile in reality, no one gives a f about the rPi you use for your Guinea pig feeder.
You might get 2¢ in about 40 years mining with my IoT light bulb. Good luck with that.
A pwned IOT lightbulb can be used to help DDOS sites. It can relay DDOS traffic, eating your own bandwidth. It can be constantly probing the other devices on your network looking for vulnerabilities, until it pwns something else and is able to slurp down your passwords and credit card numbers.
Are you seriously suggesting that having an actively malicious computing device inside your home network is no big deal?