“The downside of this now is there is a very common set of filenames that, when typed, might be converted by software into an actually functioning link to an externally controlled website.”
Since May 3, anyone can buy .zip and .mov domains from Google. Chat apps and email clients auto-link anything that looks like a domain, so a mention of a file attachment becomes a link to whoever registered that name. Phishers no longer need a lookalike domain. Google sells them the filename.