Call it the opposite of defense-in-depth. Device manufacturers who aren't thorough might allow a class of "attacks" by way of using DNS. Having ubiquitous DoH takes away that "attack" vector.
I'm not arguing device manufacturers need DoH to be jerks. Having it available just enables the less sophisticated ones to be jerky more easily. DNS-over-TLS does the same thing, it's just marginally less frustrating because it can be blocked at the network layer, at least.
I understand that allowing owners of devices to do what they want on their own networks runs counter to the whole "protect the public from bad network operators" / "protect the public from bad people" narrative. I'm in the minority. It's just damned frustrating. It's sucking all the fun out of computing and networking. It's irrational and self-serving, but dammit it makes me angry.
You see, one thing is one or two vendors misusing protocols to remove users control from their devices. Another thing is an official protocol that does the same thing. We find have anywhere to run anymore.
As bi dollar corporations and organizations are more and more "protecting" ourselves they need to remove control from ourselves.
Well, with regular DNS, you can force-route 8.8.8.8 to pi-hole and regain control relatively easily.
That's not possible with DoH due to TLS.
Yeah static IP routing is an option - for both nameservers and nefarious servers. That is, we may just have to resort to using IP blocks.
And now that it's being marketed heavily, it just gave them another reason to do it that they didn't have before ("Mozilla is doing it too!")
Devices already use pinned certificates, but DoH gives the device manufacturer a convenient and unblockabke way to resolve names against a trusted server. Device manufacturers could be jerks already, but I'd argue that DoH lowers the barrier-to-entry for being a jerk.
Consumers don't, by and large, give a damn about whether they actually own their devices or not. This is yet another reason why those of us who care about ownership and control of our own networks can't have the cool new "toys". We're back to feudalism.