A common reason, if not the vast majority of cases, is that people mix up which key they publish and which key they are actually using. I don't doubt there are

A common reason, if not the vast majority of cases, is that people mix up which key they publish and which key they are actually using. I don't doubt there are a lot of things they could do to improve the protocol, but this very common problem is fairly difficult to solve on a protocol level. I remember back in the days when people discouraged people from using encrypted disks because of the situation that could happen if the user lost their passwords. No disk encryption algorithm can solve the issue if the user does not have the correct password, and so the recommendation was to not use it. Nowadays people usually have TPMs or key management software to manage keys, so people can forget the password and still access their encrypted disks. DNSSEC software is still not really that developed that they automatically include basic tests and verification tools to make sure people don't simply mix up keys. They assume that people write those themselves. Too many times this happens after incidents rather than before (heard this in so many war stories). It also doesn't help that dns is full of caching and caching invalidation. A lot of the insane step-by-step plans comes from working around TTL's, lack of verification, basic tooling, and that much of the work is done manually.