In other words, it's not that abandoned GPL can't be forked, it's that it's significantly less likely to be forked because the number of parties that could pote

In other words, it's not that abandoned GPL can't be forked, it's that it's significantly less likely to be forked because the number of parties that could potentially fork it is significantly smaller. Particularly for more niche projects, it depends not only on a party with the same use case and licensing needs as the original author stumbling across it, but also having the skill and will to take it over and judging that it's better to do that than to start from scratch. There's so many funnels there I wouldn't be surprised if for many projects only a single-digit number of people match that description.