why does noone use LS anymore?

You can still use it. Calm down. Just because a few people don't like it any more and the large horde of lemmings is following them doesnt mean it's not viable.

There are many reasons people don't use LS.

There are some combos now that didn't exist previously.
Spectral Throw is much easier in everything.It always pierces also.
LS needs at least 3-4 damage supports to be an all-around skill.
And last but not least Leech.With such little physical damage you can't
rely on it for massive leech unless you attach a leech gem.

Basically it boils down, whatever build you try to make, whatever you try to do with Lighting Strike, there is another skill that will do it better and easier.

I use it ! Level 67 on ambush
Basicly a tunned version of permastun with multistrike to permashock.

LS had a big buff with the new mara/duelist interzone : RT and IG are closer than ever.

Going now with 3.7k life 4.2K dps (paper not counting shock stacks ...)

3 auras : determination hatered and tempest shield
lot of block ...

With all ne new nemessis mod having the possibility to kill thing at a distance is soo nice.

LS only need to be 20% qual to shine in all situations : so nice to have free pot rejuneration from the boss adds ...

5L : LS BM WED MS AFD (switch to LGOH if needed)

Because as somebody said earlier, the only thing that ever made LS playable(multistrike) was nerfed on it and now it's clearspeed is just pure thrash. I used to play a LS templar with block when it wasn't so popular and it was quite good but at this point its just a waste of time.

petrov had a really good LS multistrike build last season I used which was able to easily farm 75+ maps with upwards of 30k tooltip dps

It was a crit based build starting as ranger (think you could do shadow as well)

I don't see why it couldn't still work now