I’ve no idea what agencies are doing, but as a (mostly scientific) editor my experience is that machine translations are almost always abysmal if the goal is a decent translation that sounds natural in the target language. I’ve turned down work quite a few times on the basis that it seemed machine translated and editing it would take too much time and effort and require too many author queries to be worthwhile.
There’s just too many nuances that get lost during machine translation (at least at the moment, using the free machine translation tools that the authors inclined to do this tend to use). That’s especially the case with technical stuff like scientific articles, but I’ve also noticed it with news articles and similar stuff that I edit sometimes - the result tends to be something that needs to be extensively rewritten rather than “edited”.
That said, I could see why a translator competent in both languages might use machine translation as a rough first step before going through and carefully rewriting everything based on the original. I sometimes use Google Translate myself when I’m editing something that’s been translated by a human and I suspect there’s an issue with the translation.