Hmmm.... what if portal travel wasn't instant, but instead (sometimes in the future) it's changed that portal takes you to some dangerous mid-realm, and once you are inside through the first doorway (portal), you have to find another doorway to actually reach your destination.
And the travel through this mid-realm, until you find second doorway wouldn't be free of dangers.
This mid-realm transport could occur when some form of magic interfering asteroid is nearby, and instead of directly to your destination, portal sends you to that asteroid, and another doorway to your end destination is positioned somewhere there as well.
This occurrences could start occasionally over time, happening only sometimes, and down the line in future (with expansion), a huge asteroid could position in the system permanently, featuring a permanent barrier that prevents instant travel, and this asteroid could be large enough to also feature brand new race that lives there.