For some reason I often find papers and thesis I read in French way more interesting, well thought and presented than most things I read in English. I have a few hypotheses on why I get this impression:
1) the publish or perish culture originated from the Anglo-Saxon world. Until recently the research written in the national language was kinda shielded from it. In Japan for instance, where the higher education is modeled upon the US one, master students are expected to publish at least a conference paper. In France students generally don’t publish anything.
2) the PhD thesis are written differently. Where I’m studying it’s basically slapping three papers together with an introduction and a conclusion. This sometimes leads to awkward thesis and shallow work. Thesis (and HDR) written in Europe are more like a very well structured monograph.
3) the way to use the language is different as well. In French, any intellectual written work will use long and complex sentences (sometimes to a fault) that are cramming few ideas and their relationships. In English the style is to write short sentences, with at most one idea each. I sometimes feel I have to dumb down my writing and splitting sentences while in my native language a Proust-like sentence would be more appropriate.
The much simpler explanation is that there are way more English as a foreign language PhD students than there are French as a foreign language PhD students.
I went to a top CS research school and there were several students from China that had such a high language barrier that their papers had to be professionally rewritten by a service the university offered. Their research was Amazing but motivating the problem, describing the methodology, etc all in English just devastated the signal.
So yeah, you’re going to see good quality French writing because French is no longer the lingua Franca of science so a relatively tiny minority of non-French researchers are going to use it.