Why is the blake2b algorithm selected?

[wyj611]

I've been working on an argon2 algorithm recently. What's the reason for using the blake2b algorithm, why not SHA3 or something, because it's fast enough? Do you need to upgrade to blake3 later?

[jc00ke]

I looked around a bit and the best (potential) answer I found is this one and some of the follow-ups seem pretty reasonable. I wasn't able to find anything definitive in the spec.