JBL - almost nothing for sale, why?

I had a similar experience back in the day. You probably know this, JBL have relaunched the L100 speakers:

https://www.musicdirect.com/Speakers/JBL-L100-Bookshelf-Speakers

There are a few pairs of JBL Synthesis 4367 for sale.

yes there are some items for sale here...and even more on ebay and reverb.com.  But in general, I must assume that owners love them so much they are reluctant to part, or for some reason they arent respected as outstanding speakers like they should be, but thats just my 2c.  All I know, is that when I upgrade next time (lets say ~$2500/pr.) I will definitely audition whatever JBLs are available in that price range, new or otherwise.  <end rant>

Good for you. There are only so many ways one can reinvent a speaker.
People like to talk about the hype with cables and yet speakers get a pass. "Old" speakers like JBL make for some great music.

All the best,
Nonoise