not missing anything, but it's just one of those things about how fast orbital speeds are. yes, i know orbital speeds are around 17,000 mph. this is just another example of just how fast that is. a lot of people might be familiar with falling objects speeding up to get to terminal velocity which is kind of a speed limit for normal things. for de-orbiting spacecraft, this is just another milestone of slow speeds to achieve and not a limit of how fast it goes.
sometimes just looking at things from a different perspective makes me smile on the relative nature of "fast"