I’m not sure that’s true. I’m old enough to remember the great British bread strike of 1977 https://www.oxfordmail.co.uk/news/11045641.look-back-chaos-c...

One of the effects of the strike was that white sliced was in short supply and mangled people ended up with weird granary loaves etc as they were all that was left in the shelves. They liked them.

And from that day granary and seeded breads became a lot more popular over the bland spongy white sliced stuff.

I will say that whatever the failings of white sliced, I still prefer it to over-sweetened US bread.