Things are extra slow at the moment. Partially because many of these postal workers were simply not on the job because of the pandemic (essential or otherwise), and also for exactly the reason mentioned above. Some people might not be aware of it (or maybe everyone knows), but all of the passenger airlines are now big into the cargo business. Not sure how long this has been going on, but I've seen it have a pretty big effect with my work. They aren't just carrying mail, but much bigger and heavier cargo like furniture.

Prices of air shipping larger cargo had actually become quite reasonable prior to the pandemic, but as noted above with so many regular flight not being operated at the moment, the usual supply/demand mechanism has driven prices (and wait times) way up.

While there were no doubt some wealthy riders back in the day that purchase those things originally, I would unfortunately think that a lot of that stuff is stolen. Not trying to start a flame war, but plenty of things go missing in Western Europe and end up in Eastern Europe.