Bearing in mind that NL and SL have many of the features (and many more) of L2/L3, is there any particular reason why neither game has been fully ported?
For a very simple reason. The original game has eight skills; Lemmings 2 has
fifty-one. To incorporate L2 into a modern clone would involve coding and bugfixing all those skills and a correspondingly huge number of possible interactions between them. (Well, most interactions wouldn't have to be separately coded, as they should arise naturally from what each skill does on its own; but there could easily be bugs that only appear when particular skills are used in combination, so every combination that has a meaningful interaction would have to be tested...)
This is a huge amount of work for very little reward, since the main purpose of modern clones is to be a tool for level design, and the community has just never expressed much interest in working with the full range of L2 skills, so at the moment there's not much reason to feel optimistic that such a tool would see much use.
Of course, this isn't an outright rejection of the idea, and it might happen one day.
