People only care about Codemasters though, it's the only developer that counts for people who don't play racing games on a regular basis, and we are unlikely to see them here again. Smaller studios? like Milestone, Kylotonn, etc., nobody here would buy their games (personally I like most of them).
Simbin, rFactor, Automobilista, Assetto, ... too niche for GOG, again, nobody here is going to buy them. People who are genuinly into sim-racing would have bought into these a long long time ago on Steam.
So it's not just a licensing issue: there has to be a market for these games on GOG, which there isn't.
Older titles? GOG gets them ocassionally once in a while, like the somewhat recent Zephyr and Cyclemania games.
Personally, I would rather see GOG get older games like these, because I missed out on a lot of them growing up. So I want older racing games like these on GOG, not the newer modern ones.