The thing about an SSG is that it's so trivial to write your own (at least for the basic cases). And then you may well get more benefit after that point from retaining the ability to customize it than you would from having a generalized one that you need to wrestle toward your use-case

It's something that feels highly generic, and so programmers jump on the chance to genericize it, but may not actually be that useful to have as a thing you can grab off the shelf