You've clearly never seen Moondragon's string onesie...
Daredevil was the first show to come out and the most popular one among the Netflix shows, so I think starting by the hero and the villain from that show makes sense. I don't think it's a conscious choice to leave anyone out; just starting by the ones who will draw the most attention. And now that they've opened up that box, it's only a matter of time until they start calling more actors to come back. I have no doubt in my mind if they ever use Jessica Jones again, they will call Krysten Ritter.
As for Emma Dumont.... I don't think The Gifted was nearly as impactful or important to Marvel as the non-FOX shows. And it was never sold as a part of the MCU, so I don't think that's a priority. As far as the X-Men goes, a reboot is the best choice.