Could also be the case, but there is like 1600 TLDs these days, ranging from foo.accountants to bar.walmart (just testing if they autolink, I don’t think they will. edit: they didn’t).
Maybe at somepoint it makes sense to exclude some of the more common terms to avoid accidental linking by people that don’t use spaces after punctuation (I hate them). But could also just be an up-to-date issue, I’m just speculating.