Why is not used much more the LUA scripting to make filters?

I can think of many reasons.

1. No need to script: The discussion you refer to is back from the V1 days. No math components, no bomber, no loop, no shapes, no transforms (except a weird version of Offset)... scripting would make so many things easier. But now FF is quite versatile and many new native and advanced components has added since scripting.

2. Too advanced for the major user segment.

3. Performance issues (first scripting was slow and buggy, then it became fast and buggy, now it is slow and stable). Personally this has been very frustrating to me and put an effective stop to my scripting projects. It doesn't pay to fix and I can understand that.

4. No sharing/submissions: I think there are many scripts "out there", but they just don't make it to the forums/library for some reason (incentives, relevance, unfinished state etc). Also "unsafe" scripts can't be submitted

I use scripting a lot in my filters. I guess about 1/5 of my filters have some original component. But, as you can easily see, they are very simple components. For example, what I do the most is having a customized switch, to increase the number of choices.

As Sphinx and AndrewA1988 said, many people have no idea about how to use Lua. Me too. Even in my free time I'm trying to learn, I'm still far from making innovative components.

There are already components doing many of the things that are possible to do. Then it is difficult to think about some script doing something completely new.

Anyway......... it would be nice to make someway a library of scripting. And trying to make new components.
There are sometimes ideas that have never been developed by Filter Forge. Most of the cases for obvious reasons: they would be simply a variation of an already existing component. But they would be useful to develop some particular filter. A typical example is the non overlapping particle for the bomber. I guess, for doing it, it would make necessary to completely re-program the bomber, creating someway a "Bomber ++". We already have two bombers and making a third may not have much sense. But in some filter it would be nice to have it.