They were added, years ago after years of development. Now, they are there. Into 2 or 3 decades, they may be gone.
Abilities of hardware are evolving. Adaptation of software is also an evolving process.
Currently LANPR does not offer almost not stylized outlines (just color and a little bit of thickness).
Freestyle go a lot further into creation of a style. When a style is created, it can be reused on any 3Dscene. Maybe some adjustments are needed.
But you don’t have to deal with a setup of several renderpasses and masks to obtain an outline effect at compositing.
That is the ease of use that makes NPR renderers popular.
LANPR is the promise of a faster and easier to use NPR renderer. That is not a surprise that makes it immediately more popular than what we have.
But Freestyle may stay useful again during years.
OSL is a shading language. Into big productions (feature film), it is common to write shaders that will specifically fits the needs of production.
Instead of dealing with nodes, technical artists in charge of that is dealing with text. And most of times, he manages to obtain desired result quickly than by grouping nodes into nodegroups contained into Frame nodes.
Those topics are a little bit technical and for production that are requiring an investment.
That is not a surprise that do not correspond to major parts of threads.
It does not mean that these features are not used by people, mastering those topics and encountering no problem with them. And maybe, people who have a frequent use of those prefer to share their work, knowledge and problems on other forums.
Cycles is an addon. You can disable it if you want.
Freestyle styles are python code independent text files. OSL shaders are also, independent text files.
You just precise a path into Blender UI to pertinent text and it should to work.
You don’t necessary need to be the author of a python or OSL script to use it.
That is supposed to be easier than rewriting Blender.
You can call directly some features of renderer by using an addon and expose an underestimated ability of executable.
But what executable is not capable of : no.
You can add a post-processing executable that would treat renderer output.
But that is science. No magic.
If process requires to treat info by core features of render engine, render engine have to be rewritten.