So this is probably a really stupid question!

My integrated tube unit recently came upon some trouble. Left speaker tweeter has horrible screech. Changed position of speakers and stayed on left. Swapped all tubes and stayed on left. New speaker cables and stayed on left. Need to bring to local guy to look at but haven't got there yet. 

In the interim I take my 15 year old iPod and connect into DVD input with a splitter cable. Then unplug left speaker cable and rotate balance to the right. 

So now it seems like I am hearing all the sound that was meant to be heard coming out of one speaker. Not quite as dynamic but actually pretty soothing hearing it come from 1 point of reference. No screech. All instruments and voices seem to be there though certainly not as engrossing.

Even my wife finds the sound less overwhelming.  I suspect this question has been answered decades ago and I am doofus for asking but why can't modern sounding equipment reproduce near stereo sound out of one speaker. 

It would be much easier in many circumstances to position 1 speaker in your listening environment let alone test and purchase.

Again my apologies for being uninformed. Tried to research but didn't find any help. As they say "You only know what you know". 

Thanks, Rich
Post removed 
Um... so you're happy with switching off the left speaker and with it, the left channel part of the recording? Then leave it like that. If you have a mono button on your amp, turn it on. That way you'll get both channels through the one right speaker. Otherwise, get the amp repaired and endure both channels. Or get rid of it and buy a Sonos etc.

OP, if your question is why can’t we create a single speaker that creates stereo like sound?

my “lay” answer would be because stereo effect happens when the sound is coming from at least 2 different physical locations. So a single speaker alone cannot do that. BUT, my hypothesis is that if a single speaker PLUS a room capable of isolating and reflecting sound, then a single speaker could theoretically bounce a sound of the walls. But here is the issue... sound waves coming directly at the listener would most likely hit the listener’s ear before the reflected sound. Anyway, I could be WAY off but it was fun to think about.

I’d love to hear an answer from a sound engineer or anyone with actual scientific knowledge about the topic... unlike me. 😊
From what my mum says years ago every set up was mono before music was recorded in stereo. I enjoy listening to various old recordings in mono, the sound comes from between your loudspeakers rather than the poor early efforts of stereo where voices and say drums came from one speaker and everything else came from the other. I definitely prefer the original mono recordings when comparing them to early stereo attempts.
But when stereo recordings are good the sound from my system is stunning so for me well recorded stereo is my goal, but as i mentioned original mono recordings to me sound better than some of the early stereo recordings. I personally could not live without 2 speakers and well recorded stereo music. YMMV.
Post removed 

Brian Wilson mixed to Mono because Phil Spector did (Spector was his role model and idol), but also because he was and is for all intents and purposes deaf in one ear (his dad when displeased with them liked to smack the three boys upside the head). For some reason, the Surfer Girl album was offered in true Stereo, the only one that can be said of until 1968’s Friends, which Brian did not produce. Avoid at all costs the Capitol Records LP's labeled "Duophonic". That was the name they gave their 'Electronically Reprocessed For Stereo" mono recordings. Dreadful! 

Spector mixed to Mono because his market was singles buyers, and 45’s and all radio was Mono in the 50’s and 60’s.

The Beatles and George Martin spent a long time on the Mono mixes of their albums, leaving the Stereo mixes for an assistant engineer to knock out in a day.

The very early Dylan albums sound ridiculous in Stereo: his voice in the center, his guitar all the way to one side, harmonica the opposite side. Mono is the MUCH better way to hear those albums.

There is a group of "Back To Mono" proponents in the Garage music scene (the lead singer/songwriter/organist of The Lyres---a great group out of Boston---calls himself Monoman ;-), feeling Rock ’n’ Roll should be heard as a conglomerate mass of sound, all instruments and vocals blended into a single entity to assault one’s senses. Unless you are close enough to the stage to hear the sound coming out of each guitar and bass amp and the drumset, that is how one hears sound from a PA system.

Perhaps one Bose 901 fed both channels would do the trick.
ricmici, it is already being done and some think it is the cats meow. Google Ambiophonics 
Did Spector ever  produce anything that doesn’t sound awful? 
Here you go. A single speaker with both left and right channels included. I am only aware of this type of speaker as an in wall/ceiling type. You could check with their engineers to see what cubic volume they recommend for best sound and have your own enclosure/speaker cabinet/ tower made accordingly.
An unusual approach to an unusual question....