I'm not surprised ...
... that tablet sales are down. Anyone who's looked at the range of Android tablets available today will have noticed that there are far fewer models available than there were a year ago, and fewer of them are anything but basic entry-level budget models.
The fact that very few new models have been released in the past year also means that most of the models available are running older versions of Android, and (as is typical with Android devices) haven't been patched in the meantime.
It's just as well that I have a working tablet at the moment, because very little that's out there appeals to me at all.