Loudness - Why has the industry stopped producing amplifiers with this feature any longer?

I will say the 4 3-way level
Switches  on each of my Ohm F5 speakers is a godsend for helping get things tuned into a room just right.  That’s 3^8 or 6561 different combos. 

Atmasphere, you aren't kidding. All the unused switches in my dad's old HH Scott preamp failed. Not worth fixing. However, in the digital world having such things as room control, bass management, dynamic loudness correction and the ability to juggle your system's frequency response all by computer (no mechanical switches) are real eye openers.
All this can be done without adding any distortion and the DSPs doing it are all operating under a 48 bit system so you can lose a few bits here and there w/o affecting the sound. It is a tweaker's dream come true and a lot of fun. If you get the opportunity you should play around with a dedicated room control processor like the Trinnov ST2 which inserts between your preamp and amplifiers. On bypass it may not sound quite as good as the system without it but engage the room control and you are in a whole new world.  

However, in the digital world having such things as room control, bass management, dynamic loudness correction and the ability to juggle your system’s frequency response all by computer (no mechanical switches) are real eye openers.

I kind of agree with this, it’s the interface I have more of a problem with. Honestly, I prefer knobs. As someone who uses Roon, along with paremetrics and shelving EQ, I would really like a bass / treble knob sometimes. So, I’d like two features really:

1. A physical knob, perhaps assignable.
2. Gapless playback when EQ is changed.
   

Without this, I end up leaving Roon alone, and resort to the integrated. No complaints, but in a future all-digital world, I want knobs, not a slick touch screen. :)

Regarding Switch/Knob issues.  Yes, dusty, worn POTS and oxidized contacts on switches can be a problem.  But that is why we have DeOxit ;-)

I seem to recall the later old TacT gear allowed for user customizable settings that varied with the volume control setting.