I could be off the mark here, but I think it's a little more complicated than that. I believe Meshtastic has trademarks on the name and logo, and they went so far as to shut down a project that was attempting to allow a device to switch between Meshtastic and Meshcore firmwares.

On the other hand, Meshcore is all open, however the client apps are closed source and on a sort of fremium model aimed at supporting the developer. Mobile apps have a 10 second wait to admin router nodes, which can be removed by a one time fee ($9, I think?). And then there's a more feature rich firmware for the LilyGo T-Deck (cool standalone Blackberry-like device) which has a paid option.

I'd like to see open source community developed apps, and I don't think there's anything to stop anyone from writing new ones, other than the fact that the existing ones work well and the paid features make for a cheap an easy way to support the project.

If I'm wrong about any of that, I hope someone else with a better understanding can chime in.