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

More outlay, and more outlets. In most homes the lack of electrical outlets is a factor. The cost of adding more outlets can be prohibitive and expensive. Am sure most people who can do this kind of thing, will have mono blocks. 
 If you ever get far enough to get to this level you will have the fun of installing your own outlet because a licensed electrician will not install it. Does not conform with current electrical regulations. https://share.google/83rLotsqDXw5JYzaz
 

I had Tube MonoBlocks, loved them.

As you age, monoblocks are lighter than one big amp. 

cost's more, .... more ....

you need a balance control, I like my Chase RLC-1 Remote Line Controller with remote: volume, mute, balance, other features.

If your sources are line level, using it, you don't need a preamp.

I prefer a Vintage Full Featured Tube Preamp, out to the Chase for remote control, then to the amp(s)

While it’s generally true that monoblock amps performance is superior to stereo amps and integrated amps, monoblocks usually cost significantly more in extra casework and cabling.