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.
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.
I think that models like Granite are less known because they aren't clear leaders in any particular area. This obscurity is also another sign of how fast models are developing. If current Granite models had been released 4 years ago, they would have been astonishing breakthroughs at the time.
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 can't say what they should or should not be doing.
Generally, it is conspicuous how American companies are absent when it comes to state of the art open models. Meta tried for some time but it seems they've given up.