There are a few reasons for this: 1) there has been a slight upswing in the number of US students applying to psychiatry; 2) there has been a mass proliferation of medical school places so there are many more students applying than before; 3) the current anti-immigration stance of the administration means it is uncertain whether IMGs who require a visa will even be able to start work on time and 4) (most importantly) there has been a mass proliferation of osteopathic students and these students are filling positions in many areas that would have traditionally gone to IMGs.
There is a common misconception that psychiatry is an easy match for IMGs; this has not been the case for many years and by the numbers IM, peds, FM, anesthesia, general surgery, neurology etc have been more welcoming. Part of this is because language/culture is more important in psychiatry, there is more discrimination against IMGs in psychiatry, and because of sensitivity to the fact historically IMGs (particularly from the Indian subcontinent) who could not match into other specialties would settle on psychiatry even if they had no aptitude for it. One problem with the numbers you cite is that IMGs who are applying to the much more competitive specialties like ortho, if they are getting interviews, they are much more likely to be exceptional candidates (e.g. worked as an ortho attending in their own country or other distinctions) meaning they is a selection bias in those match rates.
There are still many IMGs who match into psychiatry at very good programs above US medical students - and IMGs who have a good command of the american language, have solid board scores, have done 2 electives in psychiatry in the US as medical students, have permanent residency or US citizenship, and have shown a strong aptitude and commitment to psychiatry in other ways (be in advocacy, education, research, leadership, innovation etc) will have no problems matching. But is certainly very different and much more challenging than it was when I was applying for residency. As I have mentioned in another thread, I no longer recommend that IMGs who do not have a green card or US citizenship apply for residency training in the US.