It is to do with how the bread is baked. Real bread, goes through a raising and 'proving' process, before being baked in a hot oven .
In 1961 the Chorleywood Flour Milling and Baking Research Assoxiation developed the Chorleywood bread making process. It involves putting lots of extra ingredients in the bread mix, which makes the bread rise fast and then steam cooking it. Here is a link to the process, its advantages and disadvantages www.bbc.co.uk/news/magazine-13670278
Personally, when I was young I loved bread and spread, but in the 60s-70s, I gradually started eating less and less, it just didn't taste right. I had no idea why.
Then 30 years ago we moved to live in a village with a 'real' baker and I learn all about the Chorleywood process. With bread baked from simple ingredients and baked properly, I began to eat bread again.
I now have difficulty swallowing supermarket bread. It turns into a sticky paste like uncooked pastry and sticks in my throat.