Apparently the standard imposes a set of requirements that the implementation must abide by thus making it a lot slower.

[0] : https://www.reddit.com/r/programming/comments/5pwgtn/hash_ma...

[1] : https://stackoverflow.com/questions/42588264/why-is-stdunord...

[2] : https://www.youtube.com/watch?v=ncHmEUmJZf4