This is for the same reason browsers have stopped showing unicode characters in address bars: it is possible to create a sequence of characters that looks so like another host name that a naive user could be fooled into thinking they are looking at something entirely different, and this was used by many a phishing scam for a while.
If a malicious poster had manufactured a unicode string that looked like microsoft.com and posted a link here, the fact that the hostname is presented in its source form would reveal the duplicity.