Why are Ayon tube amps not mentioned very often?

Has nothing to do with the quality of the product. This is a hobby of gear flippers for the most part. RE-SALE value is VERY important. Because of the lack of interest in Ayon (and many other brands) the resale value takes a huge hit from the initial purchase price. If your gonna flip gear often you cant afford to lose 40-50% every year or 2. Thats why many stick to brands that are always in demand REGARDLESS if its the best gear. (Mcintosh/Pass Labs/Harbeth/Luxman etc)
I know if I dont get a really good deal buying brand new (20-30% off MSRP) on stuff I want similar to AYON popularity (JM Reynaud, Graham, Simaudio, Sugden) Im gonna get killed ditching it down the road.  Even at those discounts Im still gonna incur probably a 20% Hit.

Ayon products are excellent. Not much chatter on Audiogon because owners are more interested in listening to their Ayon products then chatting.

I own and absolutely love a Spirit V integrated amp that sits on the top level of an Artesania Exoteryc rack with carbon fiber arms and beechwood discs and is connected to the wall with a Shunyata Sigma v2 NR l. The Spirit V drives my Trenner & Friedl Arts very well given the speakers aren’t too efficient—high quality, natural bass, mids, and highs. I would say the integrated with the stock power cord is very quiet, has a very low noise floor, natural timbre of instruments, and good separation of instruments. Adding the Sigma greatly lowers the noise floor and makes the music jump out of thin air—very spooky. There are some excellent, honest in practice reviews of the Spirit V online that can help guide curious buyers.

Depending on which speakers I purchase next, I will be going one of two directions in the next year or so: Triton EVO Integrated or Crossfire EVO Integrated.

As an aside, the owner of Ayon, Gerhard, is an absolute gentleman which makes buying his products that much more satisfying.

I have the Ayon Triton II and have the Ayon CD-5s CD player/preamp/dac as my pre-amp.  Years of experience in Audiophile components.  All I can say is with my Sonus Faber Amati Futura's, this system is simply astonishing.  By far the best sounding components I've ever had the pleasure of owning.  Triode mode is so open and warm.  Outstanding!! sound and build quality.  The system does get  warm as tube setups do and in my opinion takes about 20 minutes to bring sound full potential.  Note: Plug the Triton Amp into direct wall for best performance.  

 USA Tube Audio has superior knowledge and support.  Actually had emails from Gerhardt Hirt for room setup and general assistance sometime ago.   Wow! Couldn't ask for better assistance.   Very happy with my setup.  Mainly listen to digital sourcing.  CD's sound like analog and amazing with that dynamic range.  I also have the Oracle Paris for analog source with Primar preamp and Ortofon Cadenza  Bronze cartridge.  I've owned this gear since 2007.    Looking to get a Network player in the near future.