I don't see the problem here.
If only 10% of PS4 owners want to upgrade right away next month, that number is way higher than any stock manufactured and shipped by that time.
So of course a lot of people will end up empty-handed, preorders getting canceled left and right as well. Let's not forget producing 10mio consoles and associated accessories probably costs around $5billion and that money isn't just lying around.

The consoles seem to be almost as popular as Nvidia cards.

I still don't get why so many people preorder hardware at launch, when it's the hardest, most expensive to obtain and has the biggest chance of hardware malfunction.

Probably because most people never had those problems

Because if you preorder you can pay MSRP so not more expensive. And you can use the console for the longest time.

Same in France but it was the same with the Nintendo Switch here in 2017