In my opinion, it might actually be a safety thing, because of course here on the Discourse Meta Forum or on some Programming Forums people know how to differenciate URLs etc., but on Forums which aren’t so focussed on tech (especially Forums for non-tech Jobs, Schools etc.) many people might not notice if they’re on a site which looks the same but has a different TLD or maybe even a completely different Domain Name.
And while this of course may be user-hostile for some Forums, nobody says it has to be enabled by Default. You could just make it like a check mark which would then use a Page by DIscourse itself or link a custom Page directly.
In my opinion this is more of an essential feature which should be directly in Discourse, but of course, that’s just my own opinion.