Big ones being:
* The standards are often not detailed enough, or contain enough loose verbage that there are many ways to understand how to implement some part, yet those ways are not interoperable.
* Many protocols allow vendor specifications in such a way that 2 implementations that are 100% compliant won't interoperate.
* Many protocol implementations are interoperable quite well, converging on behavior that isn't specified in any standard (often to the surprise of people who haven't read the relevant standards)
At least this is my experience for ietf rfc standards.
Usually when there's a high disparity between the "de jure" and the "de facto", it's due to a discrepancy in the interests and the leverage, resulting in a breakdown in communication and cooperation. Laying into either then is a bandaid attempt, not a solution. It's how either standard sprawl starts, or how standards bodies lose relevance.
> They are not the only tool, and they don't carry any moral force.
Indeed there are countless other standards bodies in the world also producing normative definitions for many things, so I'm definitely a bit confused why the focus on IETF specifically.
To be even more exact, I do not know of any standards bodies who would publish what they and the world consider as standards, that would be entirely, or at least primarily, informational rather than normative in nature. Like, do I know the word "standard" incorrectly? What even is a point of a standard, if it doesn't aim to control?