I've seen these advertisements too, also only when my phone had been playing unattended for some time.
I have a (unsupported, unsubstantiated) theory that YT detects phones of "sleepers" and pushes more profitable content with the understanding it won't be skipped.
I've got a few spare phones, maybe I'll run an experiment.
I'm not sure why it would specifically be targeting "sleepers"... there are a lot of reasons why someone might not skip ads... people who are sleeping are probably the least valuable of them.
It could just as well be something super valuable -- like an unattended kiosk device playing youtube to a crowd of people.
I don't think they specifically target people who tend to go to sleep. But, having worked in the ad engineering, I can imagine they do know how often specific users skip ads and target ads based on that property.
With YT, it might be an account-specific metric. Ie: flagged as a frequent sleeper. This would not surprise me, since they track just about every other metric possible against your account.
You can have multiple YT accounts on a single gmail acct, but I don't think that'll fool them. They know where you initially logged in from. So you will likely need multiple gmail accounts to do this kind of experiment.