Themken: Freelancer free? Certainly is not. Wanted enough that there are probably quite a few counterfeit disc copies sold online.
There are quite many different rpgs sold on GOG but more would not be wrong.
It has been for some time and is available from numerous abandonware sites for download without legal challenge with numerous downloads.
I doubt anyone at Microsoft even knows who holds the license, or even if anyone could be bothered checking if the copyright is still active or who owns it. So unless someone fronts the money to pay legal to check, it will likely remain an abandonware title.
Thus, available for free, but won't be on GOG for the same reason so many older games will never make their way here.
As for abandonware legality / rights as a consumer / the absence of legal purchase options / the obligation of society to protect art - that's a big conversation topic for another thread.