Because no level scaling at all made morrowind REALLY [censored] BORING after a while with respect to enemies, when you could KO almost anything before it had time to ever hit you
Morrowind's only problem was that it did not have content above certain level, not the "No level scaling" part.
You can place non-level scaled, themed, semi-random monsters at appropriate places around the world, and make some places easier and some harder.
Some monsters should be challenging for low level characters and some for high level characters, and some can be statically leveled so that they would be extremely challenging, even for the highest level characters.
Those monsters can be placed at areas that would not cause much problem for the surrounding areas, or be at inner level dungeons and so on... So the players can find out about their position and whenever feel like a challenge go to those places and test their mettle against the foes at those extremely high level areas, and if victorious, then they would come back with ultra high level loot, and be more prepared with even the higher level areas.
This can go on for ever.