Plenty of people and businesses have their own (DIY, etc) devices that need to use DNS. I mean it wouldn't really be the internet of things, if it didn't actually use the internet...

For instance, I own a .house domain that I use for a bunch of stuff that I've programmed. It would be a pain in the ass to go change that domain out. Now take that to next level and you're a business that's deployed a few thousand devices that need to call home.

I guess all this is to say - IoT doesn't just mean cheap botnet honeypot IP cameras. Take a look at https://www.balena.io/cloud for instance