Another potential offender is the hibernation process. It's probably compressed but still writing several GB to the SSD every time the machine goes into hibernation certainly doesn't help.
For example, if you hibernate a Linux machine, then boot it up and immediately re-hibernate, there should be barely any memory to write out (since very little will have changed since the last hibernation). Yet the written data is the whole image with no regards for the fact most of the data is already on disk and doesn't need to be rewritten.