FGW▸ (as it was then) managed to change many of its fares so that a return was roughly twice the single fare without too much trouble. So why not change the rest?
Yes - and indeed congratulations to them for making that change across our area.
IMHO▸ a change that had been overdue and moved it to a system that's about right on the flows were it was done, but there were winners and losers.
As I recall it was done without causing a huge hike in fares, on the basis that most people bought returns anyway, so the headline was (or would have been) "single fares drop". But such good news typically does not stick in the headlines or memory or (as was intended, properly) did not result in huge reductions for many people so - like good news - soon forgot!
"So why not change the rest" ... because the bean counters see fares going down (all be that the ones that not many people buy), nothing really going up, and it goes against their instinct and ruling that the overall income must remain unaltered.
The change was a brave one by FGW and it has in some cases lead to an extra complexity in buying tickets for the knowledgeable . No longer get a peak return from Melksham (sorry, but I have an example already worked out) to London because you're going up in the peak and get the £1 fare back, but buy a single up and then a single back if your return is off peak. Showing 2020 figures, but our table at
http://www.mtug.org.uk/londonfares.html shows when to buy a return and when to buy singles. And this is only 2/3 as complex as elsewhere as we go straight from anytime to super-off-peak into London - not a singe train at off-peak fares as there's a gap from 07:53 to 10:02
Edit - quite a lot added. Apologies to member(s) who liked original but are less sure of the extras!