That's more of a marketing problem than a technical problem. If there is indeed a novel use case with a good demo example that's not present in OpenAI's API, then people will use it. And if it's really novel, OpenAI will copy it into their API and thus the problem is no longer an issue.
You're right that it's a marketing problem, but it's also a technical problem. If tooling/projects are built around the compat layer it makes it really difficult to consume those features without having to rewrite a lot of stuff. It also places a cognitive burden on developers to know which API to use. That might not sound like a lot, but one of the guiding principles around the project (and a big part of its success) is to keep the user experience as simple as possible.
The power of open source!