They aren't completely absent. Google keeps releasing Gemma models. Nvidia publishes Nemotron. Microsoft has their Phi series. IBM publishes Granite. Even OpenAI released a new open model (gpt-oss) less than a year ago.
https://deepmind.google/models/gemma/gemma-4/
https://developer.nvidia.com/ai-models#:~:text=NVIDIA%20Nemo...
https://www.microsoft.com/en-us/research/blog/phi-4-reasonin...
The gpt-oss models are good but there's no evidence that OpenAI have ongoing development on open models.
I'm 99% sure it was one-and-done, box ticked, and now they can be mentioned in comments like this.
Perhaps, the issue is that the pace at which they release open models compared to their closed ones, shows that they are more committed on the closed ones and are not interested in advancing the state of the art of open models.
I was going to link all of these, some are better than others, but they're all reasonably capable. A lot of these have versions that can run on modest hardware too. Granite was the most surprising I learned about recently, wasn't too good with Zed though.