Don't know about Morrowind, but in New Vegas the problem is same enemies in same places everytime.
This is a problem but where do you strike the balance between variation and credibility: a gecko is gecko and this is where they live, or overnight replace all the geckos with fire geckos?
Morrowind was clever, in so many ways
, to the point where many people didn't even realise there was levelling of general road side creatures. Morrowind hid the level scaling right in front of the player, yes, in front of, not a typo. They made it part of the plot but didn't explicitly state the consequences...
The greatest, and most obscure, threat is the Blight, a mysterious weather-like phenomenon emanating from the crater of Dagoth Ur, warping and poisoning creatures in its path, and creating diseased horrors that attack travellers and outlying settlements. — A Savant
Lowest level creatures were 'normal', a 'rat' for example, and there was always a good chance of them appearing (iirc). Highest level creatures were infected with the blight, 'blighted rat', the background story said it could happen so we all believed it. Then they mixed in the mid-level 'diseased rats' just for variation, disease happens, I'll believe that. Genius. Also, at least some areas had the possibility of two different, but equal in level, creatures and not necessarily hostile ones. More variation, it felt totally natural.
How do you think NV would feel if it had another type of creature mixed with the geckos?
Edit:
Forgot. Levelling is great if done correctly, sadly Beth. has forgotten the tricks to success of late.
Levelled loot is passable, levelled unique items is a farce.