It’s one of those situations, I think, where one cannot eat one’s cake and still have it (I struggle to understand that phrase the other way round). Model railway production has vastly improved but customer expectations on availability may also have to change.
From the 1920s until the 1990s (barring World War II/Irish Emergency I) model railway products were freely available but from a very limited range. Hornby Dublo for instance, would only furnish a very limited LM region layout with an 8F, 4MT, Duchess and class 20. The catalogue hardly changed year on year - and only by the last few years was Super Detail rolling stock produced. Otherwise the standard of HD models hardly changed from 1938 to 1968. Factory jigs and personnel at Binns Road were dedicated to the same task for decades.
The business model has changed now, and model locos are produced in shorter runs but with increasing prototype fidelity as years go by. Compare a Hornby loco of the 80s with today - and the standard is changing all the time. To go backwards is pricey and inconvenient. As the business model changes, so must the purchasing one. And the sad reality is that you have to buy it when you see it.