Early in my career as an EE, I learned that your world could suddenly be upset and swaths of components could suddenly become unavailable to the small manufacturer because an auto company or some other massive customer got preference, so the majority of parts went "on allocation." Meaning that the production runs were allocated to certain customers and if you were lucky then you got the leftovers. You could suddenly not be able to built product for a year because critical parts just couldn't be found on the market. I remember one vendor selling a part that normally cost around $16 for over $400.

It's not specific to the Pi: this happens everywhere.