They release their stuff, but only under (significant) community pressure, and they try to do it in such a way that interop becomes harder and harder. Some parts they never release, because 'reasons', but are suspected of containing large chunks of FOSS used outside of license.

And then there is crap like this:

https://www.josefprusa.com/articles/open-hardware-in-3d-prin...

Bambu is fantastic hardware but they're doing the exact same thing that DJI did in the drones field. A few more years and Prusa will have gone under, because it is impossible to compete with Chinese state subsidized companies whose sole purpose it is to dominate a market where they take something that has been community built and then embrace and extend it in every way possible to kick the door shut behind them. All of course in your best interests.