Secondly, the root server operators have no control over the cryptography. They get a zone file and they serve it.

ICANN only runs the key generation ceremony which is scripted to prevent any single entity from tampering with the keys. ZSKs are generated a few months in advance and used by Verisign (the root zone maintainer) to sign the root zone. No one gets to see the private part of the KSK. So there is no way to compel ICANN to produce bad signatures.

Finally, glue records aren't signed!

https://www.internic.net/domain/root.zone

The people responsible for running the root stores do. And when CAs screw up, they are nuked from orbit--this has happened a few times. And they can be proactive: when Kazakhstan announced they would require all TLS connections to be MITM'd, the browsers promptly added the MITM certificate to the root store with the explicit distrust bit set, meaning that the resulting certificate error can't be clicked through, effectively breaking the internet if you tried to use that for MITM (which put the kibosh on that plan immediately).

And for another thing, I wouldn't trust the people who run the nameservers any more intrinsically than CAs. After all, the TLD that runs most of the commercial internet (.com) is run by a company that had problems when it ran a CA. There's no way to route around an untrustworthy TLD operator, and it needs to be recalled that many TLDs are literally run by state governments. And several of those governments believe the privacy of their citizens to be a bug, not a feature; giving them a more prominent role in securing privacy is not a good thing.