Mono Blocks / why are they not more prevalent? + Wyrded4Sound SX1000R

@mashif - Often the transformer is shared, even in dual mono stereo amps, but not always (e.g., BAT). When the transformer is shared, there are greater chances of inter-channel modulation, crosstalk, and noise.  Whether any of that matters, or is audible, and how good the amplifier sounds is likely based on many other design choices, as well as the system it is being played in. While housing the amplification components for each channel in their own individual chassis reduces the likelihood of certain undesirable effects, it doesn’t guarantee success since there are good and crappy sounding amplifiers, both stereo and monoblocks. 

@mitch2 

Sharing a transformer would not qualify as dual Mono to me. I was thinking of my Bryston 3B Cubed that has separate transformers for each power supply. It's two separate amplifiers housed in one chassis that only share a power cord. 

I’ve had quite a variety.  

From a massive 70’s Kenwood receiver a Sony wee compact dual mono (really!!) simply shined …which my daughter and a succession of two roomies will be happy to attest to, through Conrad Johnson tube preamp and dual monos, through a succession of Naim Classic separates but not dual monos…100, 200, 500, to finally using the most astounding of all, ATC 50 active speakers with an amp for each driver, plus 2 REL Gibralter subs. I think the main thing is less complex load in the path between the wall socket to each speaker always sounds better, closer to the recording.
Perhaps the biggest proof for me was a second system. A little Linn Classic that I bi-amped years later. After nice comments from the shop i added an LK140 (cheap,used one). After fiddling speaker cables to Linn for the Classic to tweeters, and Naim cables to woofers of my old Linn Tukans) it gave me a wonderfully improved sound in every way!  All i can say is that i jammed away the entirety of “Hamilton”, dancing delighted to Lynn Miranda Manuel’s performance most of time. And it’s not short. There was a single big old REL in the chain too.  
I like to dance, but this was ridiculous!

It was not the pure tonality of each string and horn of my Naim/ATC/REL setup, but adding the bi-amp signal clarity let every bit of Linn’s charm sing, sing, sing. 
Frankly, I’m not sure I’ve had any better experience of recorded music.  I’m always happy when i listen to this little system. It’s not the tonal purity of my flagship, but absolutely wonderful and a world better than before bi-amping.  If it’s adding color it’s a great one. 

Go figure.  I’m just believing my ears. 

Like pretty much everything in this world, just follow the money. 

My current Tube Monblock amplifiers do sound different from my equal level quality tube stereo amps I moved from to the mono amps. And, different yet again from my last two dual mono solid state stereo amps. The channel separation, instrument placement, sound stage presentation, and layering was immediately evident with my current monos.  

I'm fairly convinced now it would likely take a much more expensive dual mono stereo amplifier to provide similar results to my current monoblock amps - fwiw.