HN users have varying views on what crosses the line into spamming. I think if your comment had done more engaging with what's intellectually interesting in the current thread, instead of sounding promotional, it would have done better. It's also likely that some HN users are sensitive to the issue of profiting from prisons.

It's fine for established HN users to bring up their projects/products in an on-topic way, as long as they don't overdo it participate on HN for more than just that.