Older Jazz recordings

I’ve noticed that as well. I have always thought some of the engineers were so used to putting the players close to the mic in mono that when stereo came along they added another mic they just split them putting some in front of the left mic and some the right. Some engineers were not creative when stereo became a thing. Then, as I am sure you have heard there are those who understood the potential and pulled the mikes forward and in and captured the sound stage... producing some of the best recording of all times.

I have been surprised how many uninspired engineers there were. I was listening to one album with absolutely no sense of soundstage. I read the album cover. It was marked as a ambiance extravaganza! Advertising how it captured the great orchestra an the hall it played. With great pride on the back they showed the position of the entire orchestra how they participated small groups of instruments and put up barriers around them! The recording was truly hideous and captured nothing from the venue.

A bit off topic, but a great story:

Then there was this violin concerto where the commentator on the rear of the album gushed over the performance of the violinist, covering the entire rear cover... but all the words of praise were of the tone of the instruments (attributing it to the skill of the violinist). To me the description was not of the performance, but of the instrument, and he had described the sound of a Stradivarius exactly. No mention of it on the cover... but a search on the violinist showed he played a Stradivarius.

It's called mono.

Right, the center image are mono recordings.

Alternatively, early stereo had three channels, left, center, right. So you hear hard left and hard right instruments.

Some of the older Jazz recordings aren't the best example of stereo or mono.

There are mono recordings that are just simply bad, but a good recording is more believable to my ears. Stereo or mono, it's still just an illusion. 

I don't stream and just play period LP's. Some of the best straight ahead Jazz  is 50's mono recordings. Overall SQ can be just so-so on some. Others, can be sublime.

Cannonball Adderly- if you like any of the  divas of that period,  1962 Nancy Wilson/Cannonball Adderly. Great mono example if you get that from your streaming service.

Agreed with above comments about microphone positioning. Stereo recordings from that era didn't need to sound so claustrophobic but in most situations, engineers were fighting room conditions like reverberation and echo. The late 1950's RCA Living Stereo recordings were simply three track recordings but they were recorded in halls with desirable acoustics. Most likely, RCA were using Telefunken U47 microphones versus something on the cheap.