Programmers do have to agree on ways to represent information when interfacing different systems. Right now for the web, that is HTTP APIs.
There is a pretty powerful religion pushing "true REST", i.e. emphasis on using the correct HTTP verb in the proper way in relation to the type of entity being updated.
To me, that is enforcing a very basic general (CRUD) type of knowledge representation for the programmed web. I think it demonstrates that the instinct for a common language is there.
You can also see serious KR use in certain domains like biomedicine.
One area I have been thinking about applying KR is in defining information systems and programming languages. The reason I want to do that is because there seems to be quite a lot of overlap between a very diverse set of programming languages, and also because I want a format to be able to represent algorithms that can serve as a basis for a type of open source operating system. This operating system either needs to force everyone to produce code for a certain programming language or common lower-level virtual machine. OR: it can use a higher-level semantic metalanguage (maybe based on description logics) and then people can program that in the language they choose (perhaps something most suited to a particular system or domain).
All of these are programmer use cases. I think more and more of this general purpose type of knowledge representation will inevitably start being applied by programmers.
One key reason we don't see it applied more often I believe is convenience. You need a convenient representation and convenient tooling. Most of the semantic web or more generally KR tools haven't focused on that enough, which is understandable because the core requirement is machine-processable exchange. I think the trick might be coming up with a way to embed a compact KR more directly in general purpose programming languages or data formats, or translate automatically to and from domain representations to a KR format.
Another idea I had besides building an operating system on top of a DL (translated to and from different programming languages or representations, serving as a common metalanguage) was to try to popularize semantic computing at the same time as you popularize a standard for the metaverse. https://github.com/runvnc/vr