When I become king of the United Continents, I will make a new rule:
If you don't publish high-quality updates for your software for one year, it will become open source automatically.
Mm. I think "any" update would be sufficient for 95% of cases, doesn't have to be high-quality.
Even if it's just the copyright date changing at least once per year, that tells you one specific named entity is claiming to care about it: when nobody does even that much, everyone automatically has the right to do whatever they want with the software.
Which reminds me, I need to update the copyright date on my website…
When I become king of the United Continents, I will make a new rule: If you don't publish high-quality updates for your software for one year, it will become open source automatically.