What would be the information the oven can expose over thus a channel? How often I cook? How much energy I use for cooking? The oven will not even know if I'm at home or not if not used. I can't think of any critical spying done that way?

Of course if the oven had cameras and microphones - but then again, the bandwidth of a covert channel would be rather limiting.

Oven usage data is probably extremely valuable for advertisers.

The things you can do with statistical methods nowadays might blow your mind if you think there is not much information in oven usage.

You could infer likely occupancy periods of the home, since obviously if the house is empty no one is pushing buttons on the oven, and use some basic priors (9-5 jobs, x number of kids) to develop what is likely a pretty accurate model that would be profitable to sell to advertisers. Perhaps there are sensitive voltmeters on the power supply that can detect usage of other devices on the same circuit. Not to mention that it is yet one more channel of information alongside the flood of data being generated about you and your home by the rest of the devices you have incorporated into your life, and these things tend to have superlinear benefits when combined a la "multi-task" ML contexts. This is not an exhaustive list.

Moreso, you never know if there's some logic bomb inserted in the response.

And it's not at all far-fetched. We have the Sony PS2 Linux yanked away after it being a sold feature. And with a joke of a response to that, indicates that any internet connected device is a rental to the ever-changing terms of the real owner.