A standard starting item in some packs is "a bag of 1000 ball bearings." Now, I am still a D&D newbie, but it seems to me that the cart is way before the horse here. Heavy-load-bearing rotating shafts did exist in the pre-industrial world (e.g. water wheels, capstans, trebuchets), and there were apparently crude wood-and-wax or plain brass bushings that served the purpose.
But whence ball bearings? I suspect that the minimum technology to make a ball bearing possible is a lathe, as they are machined down from slugs cut from rod stock. Lathes have existed for millennia, but were certainly not widespread until the last few centuries. Likewise the technology to make ball bearings necessary, i.e. heavy machinery rotating at high speed, does not appear until the industrial revolution. Furthermore the size at which they would be useful for trap-laying indicates small-scale, high-speed applications. There is also the matter of the implied mass production of steel, such that a thousand of these things is just something one can get with relative ease (emphasis on the relative).
I understand the artificer class may find some use for them, but I believe the bag of ball bearings have been around since 1e. Their availability (not to mention their canonical naming) indicates a level of industrialization that I just don't see in the Forgotten Realms. Yes, they could be magically created yada yada, but magic is relatively rare and expensive, so why use the magic to make bearings when you could use it to do the thing?
To me, the economics of it just don't indicate the plausible widespread existence of ball bearings. Is there a canonical answer of which I'm unaware? I haven't seen this raised anywhere before, so I've seen no such answer.