The person who subbed DOESN’T WANT TO BE RECOGNISED
Currently, those people will tend to sub/resub whilst the channel is offline. Because they don’t want to be recognised.
Further more, a “big partnered caster” might choose to not notify their sub, because of the eventual “when are you streaming next” spam that might occur.
This makes it hell of a nasty to manage, Twitch side, since TWITCHNOTIFY has been on the way out for a while anyway, since the new resub stuff came in, that was all USERNOTICE anyway.
Thats just two examples of ways/reasons people want to sub anonymously. And a caster is better off honouring their lurkers right to lurk, than calling them out…