.....First:
I can remember trying to make journeys using British Rail in the 60s and 70s - usually dirty(often filthy) coaches (that's inside as well as outside), frequent cancellations, weekend trips were a joke - no substitute road coaches, just take your luck with diversions, no published arrival times.
No I am sorry but that just is not true whatsoever.
There were Special Traffic Notices published in advance, and all timings for diverted or altered trains were notified to the Passenger Commercial dept who prepared the various posters which were displayed at stations. Please do not try to tell me that is wrong because part of my job many years ago was to put up and take down these posters, and later on I worked in the train planning section doing the Engineering Work alterations. These were not that complicated given that many services did not start properly until after lunch, and pretty much all engineering work finished for 16:00.
There were even Sunday timetables printed and supplied to the public.
With regards to "dirty (often filthy) coaches" comment may I point out that it is passengers not Railway staff who make the coaches dirty. Indeed an excellent cartoon appeared in Railnews (in the 80s I believe) along the lines of your assertion. A train could leave the Carriage Sidings in a good state of cleanliness and within a short time become akin to a rubbish tip, hence why some TOCs now have roaming cleaners.
In the 70s, the Country was within a downward spiralling economy which meant that the Railways along with other Nationalised Industries were used by the Government as a means of controlling money and finance. Thus the Railways were the first to lose out when it came to money, especially when compared to the Miner's who used emotive historical arguments to win ever greater pay rises - the money for which had to come from somewhere, in other words the Tax Payer - or had large industrial muscle such as the T&GWU which could be, and indeed regularly was, used to bring widespread Industrial disruption. The fact therefore is that for pretty much all of the 70s the subsidy paid to BR was falling in real terms (remember inflation in double figures and 18% pay rises ??) and the Railways were given no latitude. Any sort of "Improvement" was treated by the Government and the Treasury as "Investment" which meant that the money came from a different and much smaller budget.
We were thus locked into a nightmare situation that whilst it would not have cost much more to relay a section of track in long welded rail which would have generated considerable savings, financial dictates from Government resulted in us renewing like for like 60-foot track panels with all the attendant mid and long term maintenance problems these brought. You can add to that the ever increasing costs for maintaining that track as well, truly a spiral of financial decline
Government restrictions on us recruiting, as well as the holding down of Railwaymen's pay meant that it was difficult to recruit, and more difficult to keep staff, bearing in mind that you could probably earn twice as much at British Leyland, work a lot less harder and have your weekends free.
So within this bubbling pot it was extremely difficult for us to recruit and retain carriage cleaners as this was and is still regarded as one of the worst jobs possible. You, for example, want clean carriages but I very much doubt you would be willing to go out cleaning them for a pittance ?
Given that what would your decision be - send out a train not completely clean or cancel it ?
I note also your throw away comment on cancellations which is normally the sign of someone who has taken this comment from the generally publicised urban myth about Railways in the 70s. I reckon on having done somewhere in the region of 250,000 train miles a year in the 70s, and I recall, and my records show, very few cancellations or indeed failures.