If they want to continue to harvest their customer's data they can provide those customers with support.
Also, those Google devices aren't free. You buy a Google device, get no support, and the devices are updated for way fewer years to boot.
You keep mixing things up. The topic is the viability of high touch GMail support, not support for Google's home-grown devices.
Amazon is similarly an order of magnitude fewer users than Gmail accounts (and tends to address this issue by pushing the hard-to-address auth problems onto the seller... There are known exploits for just pushing exorbitant costs onto the seller via buyer fraud). Amazon has a couple hundred million customers... Gmail is in the billions.
I am, perhaps, just simply old enough to remember when not everyone could have a Gmail account. Low touch customer service that works 99 plus percent of the time was necessary to open the floodgates for free. I have never seen a practical explanation of how to scale providing the service otherwise. There's room for improvement, but (a) every simplification of authentication must be balanced against how it can be abused to steal accounts, and (b) I cannot conceive of a solution that would rival high touch customer service, and that scales to the billions. If one exists, I look forward to being extremely pleasantly surprised (having myself been on the receiving end of losing my phone while away from home for an important event: yes, it really sucks, Google's trust model is they trust you zero without some corroboration if all you show up with is the password). But I've watched them hammer at the problem long enough to suspect it's uncrackable at the billions-scale.
They simply choose not to.
I'd be interested to see a workable solution but, to-date, I never have.
Yet somehow companies of similar scale like Amazon, Apple and Netflix manage to provide robust customer service.