What's up with the mono turned stereo mixes???

I've been listening to some jazz resisues on CD and they appear to be original mono mixes turned stereo or really weird stereo mixes. It's like, when they made the stereo mix each instrument either got the left OR right channel, but not a mix of both. So, you've got the one trumpet over here and the other trumpet over there and then the drum solo which is a mono mix from one channel.

It's good music, but ???

I don't know the answer to your specific question but I'll share some insight. Being analog based and having recordings dating way back to mono days up to current recordings, those that were electronically re-engeneered to stereo were always labeled as such. I've never been satisfied listening to these and much prefer the mono recordings. Some of the instruments lacked a specific location but did come from either left or right but most of the information remained mono. It just isn't satisfying. I think what you have is another type of recording that irritates me. I've been conditioned, right or wrong, to want the drums in the center with a bass close to the drummer. I've also been trained to want to hear a left and right aspect to the drummer. A few of my early true stereo recordings place the drummer to one side. I'm sure this is the way they meant to do it but it just doesn't feel right to me. These same recordings tend to place other instruments clearly left or right with very little of a balanced stage exhibited. While I'm not any type of recording historian I believe that these were minimalist mic'ed recordings using mono mics. Later recordings which I prefer began using stereo mics and still were done minimally. The result is a more realistic staging of the players. At least this is how I've been trained to enjoy them whether it's better or not. For some reason a stage left or right drummer is a big turn off for me and these recordings go unplayed. I'll be anxious to read any other postings to your insightful thread as I'd like to know more about this subject.
I always choose mono over the usually bad stereo mix on those recordings. I don't know why but it seems to sound better quality wise.