Has it been suggested by anyone yet that Google is pushing for DoH because those DNS-typo advertisers are a competitor to its ad/search hegemony and eliminating them as a business model helps Google's bottom line.

I am certain it's been suggested. But I can't see Google's motives I can only see its actions. If you do good things whatever the reasons the good things stay done while the reasons die with you.

A few minutes walk from me some people opened a gelato place. You go there, you buy some gelato. Nice. Warm summer evening, drop in, buy a cone, delicious. I am 100% certain that by selling me frozen desert they get money! Their plan may not specifically have focused on me enjoying this at all. And yet, since the effect is that I can enjoy desert that's exactly what I do, and I don't begrudge them their money.

I doubt it, from what I know, the money the ISPs make from typo-searching is barely noticable, mostly a leftover from when ads where valuable.

You can say anything Google does is because it ends up pushing its own ad model, but I don't think many users would actively want ad results to show up when you would regularly get a NXDOMAIN.