[T-A]

Maybe not surprising at all. The author open-sourced Orbiter in 2021 [1]. It's MIT [2], so anyone can pick up from where he left off and create a commercial version:

[1] https://www.orbiter-forum.com/threads/orbiter-is-now-open-so...

[2] https://github.com/orbitersim/orbiter/blob/main/LICENSE

[Suzuran]

DocMart hasn't abandoned it, it's still under active development. Open-sourcing it was to get more people involved because he couldn't do everything solo anymore.