Consider this question:
How is that question off topic when reusing blowfish algorithm to implement bcrypt isn't? Does the fact that I include code samples mean it's automatically off topic?
Migrating crypto questions like that to stackoverflow is basically a death knell for those questions. The question is about how to make an existant ChaCha20 implementation give the same result as HChaCha20. There's a chacha tag on crypto.stackexchange.com - there isn't one on stackoverflow.com. There's an openssl tag, sure, but just because you know how to use openssl doesn't mean you know anything about the internal structure of ChaCha20 vs HChaCha20.
More than that, the problem is one that should be duplicatable in any language. That I posted my code samples in PHP is irrelevant because the question is language agnostic. Would the question have been on-topic if I had posted the same code in 10 different languages to prove how language agnostic the question is? And if the question is, ultimately, language agnostic, I contend that that is further evidence that the question is on topic here and off topic on stackoverflow.
And not only do I contend it's language agnostic - I also contend that it's library agnostic - that this "issue" is duplicatable in any ChaCha20 implementation, be it OpenSSL's, libsodium's, BouncyCastle's, etc.
Of course there are certain practical considerations when posting code samples in 10 different languages using ten different libraries. ie. the longer the question the less likely people are to read it. Posting a question is a delicate balance of making it succinct enough so that people read it yet detailed enough so people actually understand what you're talking about.
I suppose I could have omitted code samples all together but tbh I think that would have made for a question that would have been nigh impossible to understand. Maybe if I'm only going to post code samples in one language PHP isn't the best language to be posting them in. Python is taken more seriously in the crypto community than PHP (as evidenced by the fact that the code samples in the Ed25519 RFC are in Python) but, sadly, I know PHP better than I do Python. And tbh dismissing PHP on the basis that it's PHP is just prejudice on everyone's part.
Consider https://stackoverflow.com/q/32161720/569976 . That's a crypto question that's on stackoverflow but that question belongs there because it is not language agnostic. The question I posted - that I contend was naively migrated - is language agnostic.
Another example that crypto related questions / answers receive far less attention on stackoverflow than crypto.stackexchange.com: https://crypto.stackexchange.com/a/21104/4520 vs https://stackoverflow.com/a/21289989/569976 . The former quotes the latter. It links directly to the latter. The latter was posted before the former. And yet the former has 34 upvotes whereas the latter has 4. Language agnostic crypto questions on stackoverflow do not at all receive attention like they do here and if y'all are going to migrate language agnostic crypto questions to stackoverflow then y'all might as well just close them all together because, barring a bounty, migrating them to stackoverflow is a death knell.