I don't know the details and also I don't know to which ISS cameras you compare, but those suit cameras have to be robust, flexible, likely low power consuming

I don't know the details and also I don't know to which ISS cameras you compare, but those suit cameras have to be robust, flexible, likely low power consuming and bring a good reception. The interference with this analog technology isn't that bad. A human viewer can filter those troubles in real time. Compared to a digital video stream, we would have had green blocks, frozen images, delays etc. at least when using the same bandwidth. There could be improvements for sure, but maybe it isn't worth the effort.