Umm, wasn't he imprisoned for life? Had Thor Dark World not happened, Loki would still be in prison.
That's the thing, he escapes and is now in his own series saving the universe as a hero etc... and I've never seen anyone complain about him not getting punished the way they have with Wanda. But I guess it's still unclear what his actions at the end of Loki the TV show will result in, I recently saw that they're currently filming season 2 so hopefully it's not too long before we find out.
Either way I'm happy to withdraw the comment, it's getting a bit off topic at this point.