If you look at
the spousal processing timelines, you'll notice that there are several embassies whose minimum processing times start in excess of six months. Not sure about the reasons behind this - maybe a huge number of applications, maybe an embassy that is only staffed part time, maybe increased processing times for background checks and such, maybe a higher percentage of interviews required. All of this is just pure speculation on my part, of course, but I suspect that for some embassies there may simply be increased scrutiny of applicants/sponsors. Not saying that's the case for Nairobi - but it could be an element.