The long tail exists and is very long--longer today in a world with Amazon--and that they don't have to write a screenplay adaptation and can instead eat and keep a roof over their heads while they write the next book is a feature, not a bug. It accrues over time and the gap between personal prosperity and precarity grows over time because the back catalog keeps selling.
1. Yes, and many never succeed in their life but getting royalties from old works is something to keep you going and a reason not to give up.
2. Those successful works will not bring in the money for decades, just a year or two and then slow to a trickle of royalties. Having a single work which sells well does not mean you are set for life, just means you can breathe easier for awhile.
3. Piracy would not be an issue if that were the case, many already do not pay for it. Sure many say that is because they don't want to support the industry but they are also taking from the writer much of the time.
4. But anyone can now monetize it in all those ways and now the author has to compete for their own work on top of all these extra business dealings and working on new output. And even then things like a bad movie version (which author has little control over) can seriously hurt future sales. This is just trying to turn artist into a brand and not many have pulled that off successfully.
5. This is not really a condition for your point and not even a point.
6. Generally rights are not sold, publishing right are sold to the publisher for a certain number of years and after that time is up the author is free to go make a deal with another publisher or self publish it or what ever they desire.
1. Many artists are commercial failures for over two decades, but eventually succeed;
2. These artists’ newer successful works don’t result in income equivalent to working a full-time non-creative job for that time;
3. Fans will not pay them for the old works without the threat of legal action;
4. There is no other way to monetise the old works by e.g. recording a commentary, audiobook, screenplay adaptation, manuscripts, compilations, special editions, etc.;
5. Artists don’t pander to current trends only because they know they might be able to make some money over 20 years later;
6. The money they will get paid in royalties under a contract where they sold the rights to a publisher when they were an unknown nobody is greater than the amount of money they would make selling it directly in the public domain after becoming commercially successful.