I just had a look round the github about this, as the suggestion has come up before.
Apparently there are privacy concerns about this suggestion, that people could use lists to stalk someone etc.
There was an alternative suggestion that people could mute someone on the main timeline but not on the lists, I don't know if this is being implemented though.
If you use RSS, one workaround is to follow the account through RSS instead. This will only show its public posts however.
You can follow Mastodon accounts through RSS by going to their public profile page (click on their profile avatar to do this), then add ".rss" to the end of their public profile page URL.
For example you can follow FediTips through RSS at:
@Christian@cybre.space On Misskey you can do that—add people to lists without following them. I actually prefer that because... sometimes I just want to see what someone posts without sending the "Heyyyyyyy, I'm following you nowwww, isn't that nice??" notification.