if the idea is to protect users so that you don't end up clicking on https://news.ycombinator.com.myhackerdomain.com , you then open the attack of a platform where they offer custom subdomains, and you have
if I make them look the same, and the address will hide the subdomain, it looks like a step backwards in securing the web
now, imagine the actual platform has a payment section, and I create a fake subdomain that looks pretty similar, email you, boom, I get your cc info because I tricked you into entering new cc info (assuming your scenario of someone being distracted)
Only supposed "trivial" subdomains are hidden, such as www. and m.
Anything else is still shown. fake-original.blogger.com will still show up as fake-original.blogger.com because fake-original. isn't a trivial subdomain.
I still think it's a stupid move, though. It's a simplification that is incredibly unnecessary and may be harmful when dealing with the rare site that doesn't treat www.domain.com and domain.com as the same.
https://original.blogger.com
and then
https://fake-original.blogger.com
if I make them look the same, and the address will hide the subdomain, it looks like a step backwards in securing the web
now, imagine the actual platform has a payment section, and I create a fake subdomain that looks pretty similar, email you, boom, I get your cc info because I tricked you into entering new cc info (assuming your scenario of someone being distracted)