This is my thought as well. At this point, this long after the bombs, I'd expect nearly every suit of power armor to be either stashed away some faction's armory or scrapped for parts. A power source that lasts for hundreds of years would be one hell of a piece of tech, I could easily see one being taken off a suit to power a settlement or something like that. Really there's plenty of reasons why a suit may not to have it's original parts.
Not to mention that all these suits have been sitting around for 200 years, most have certainly not been maintained on a regular basis. Even the most well designed machine can wear out and break.