Since ODoH they could perform such attacks without being spotted by ISPs.
Also, if the reputation risks is the only thing which could prevent them from doing so... it is not the security we expect from the cryptographic protocols. A subpoena/warrant could be a more "colossal" threat to their business.
I'll give you that - based on a brief search - this does not appear to apply to other browsers yet.
They risk losing their status as a trusted CA.
There are tons of goals more important than the trusted status.
Killing Osama, arresting Silk Road, performing or exposure of election fraud, ...
Losing of the status might happen sometimes later while the traffic interception/modification is what they can do right now. And it could be ordered by someone who do not care on those statuses at all.
My home LAN gateway is blocking DoH because the hassle of issuing enterprise-based intermediate CA is not worth the effort to do a Squid TLS transparent proxy so that one can “Pi-hole” to block stray DNS/domains.
This means my own set of authoritative DNS servers.