I think a fundamental issue is just that there are so many train companies. I don't think many (any?) other countries have quite so many, even JR isn't just one company. Even when individual companies put some effort into a renewal making things easier, when the experience starts from first finding out even which company to book from, there's a huge barrier to entry.
I think it is possible to define a booking standard so a meta provider could handle things, like trip.com etc for flights, maybe someday.
When Norway (unfortunately) privatized and tenderized* the railway, they at least made a provision that every ticket should be purchaseable through a government owned entity. Which means you can use the government app ("Entur") to travel plan and purchase, even between operators and even modalities (trains, busses, trams, etc).
* (using the word wrongly), and it was a hack job. The existing operator is still owned by the government (NSB, renamed to Vy), but then had to bid on contracts to win their existing lines back. Which they of course were predetermined to lose most of, otherwise all that work from the right side government would have been useless.
Of course, NSB then also couldn't have any advantages having been the sole provider from before. So men in suits decided which IT systems they were allowed to keep, and which should be the basis for the Entur app/system.
I came in as a consultant at Vy to reimplement what got severed, without having any prior knowledge/advantage.
So much weirdness, and so much waste
The UK had/has far too many companies following the 1990s privatization, but any company can sell a ticket on any route -- online, at a ticket office, or using a machine.
I don't know the rules, but at least the company with the cheaper/slower trains from London to Birmingham shows their faster/dearer competitor when searching, and vice-versa, although you do need to search "London Terminals" to "Birmingham Stations" rather than specific stations. (The trains use different stations.)
I don't have a better way to validate my claim, so please feel free to correct me, but it seems like Switzerland and Japan have a similar concentration of transportation companies per 1000km² [1], yet with the SBB Mobile App [2] you're able to book any journey within Switzerland (and even cross-country) by just selecting origin and destination.
I think there's no excuse to just have a better transportation system, and I think every country should aim at excellence in this field (along with having public transport arriving on time).
[1]: https://www.perplexity.ai/search/08b4e2d1-f249-4827-8b69-2f3...
[2]: https://www.sbb.ch/en/travel-information/apps/sbb-mobile.htm...