http://6hasakffvppilxgehrswmffqurlcjjjhd76jgvaqmsg6ul25s7t3rzyd.onion/
As well as adding another means of censorship resistance, a hidden service gives an alternative trust path that doesn’t rely on certificate authorities nor DNS infrastructure.
https://bitcoincore.org/en/2020/03/27/hidden-service/
Archived:
(1) https://web.archive.org/web/20200331063411/https://bitcoincore.org/en/2020/03/27/hidden-service/.
(2) https://archive.vn/itTxT
In case government decided to hunt and shut it down, others might want to archive it as well.
Obviously, as stated, the main reason is to resist censorship.
https://www.reddit.com/r/Bitcoin/comments/fruxr2/bitcoin_core_shifts_to_dark_web_to_resist/