The issue about using a portal to Demonreach is that with a Warden in place and it’s defences active you can’t. Odin and Ferrovax can block the NeverNever for Chicago and I presume Alfred can for the much smaller area of Demonreach.
Even without its full defences active it isn’t an easy place to portal in. Maeve presumably was able to do so to bring in Peabody (which is the current popular theory) but wasn’t able to do so in Cold Day’s. Mab suspected her for decades, but in Cold Day’s she was fully recognised as a threat. If there is an Arctis Tor route, previously available to her, it wouldn’t have been available by Cold Days. Mab had a spy in Maeves court the Redcap, so if he reported her interest in Demonreach with the Peabody incident, that would have been closed to her.
Thinking about it it is entirely in Mab’s character to have allowed Maeve to use the Portal as a test to see if she was connected with the Black Council.
There is at least one other portal to Arctis Tor used in Proven guilty, so Maeve, so Peabody portalled from Edinburgh to Chicago, got a cab across Town to the Proven Guilty Portal where he was met by Maeve outside Arctis Tor, who then took him and the Spiders via the Arctis Tor Portal to Demonreach, taking him back.
The fact that there isn’t a more direct portal to Arctis Tor than Chicago or at least a safe one for Peabody is either noteworthy or lazy writing by Jim. The whole reveal of Peabody would have failed otherwise if a different route was available.