Or alternatively, they took forever to do it not because they don't like generics, but because they are super conservative with design and wanted to do it right.
If it's so damn obvious/you're so brilliant where's your proposal dated Jun 2010 (your 'decade lost') that "solves" generics?
It may not be surprising to everyone. Trouble is that the people who are not surprised now are the ones who sat back and only watched, preventing their knowledge from making it to the project.
Luckily for Go, a small team of domain experts decided to do more than sit back and their efforts are how the latest proposal was reached.