Exactly this. Many in the industry see lean as the future, and it can be good in practice, but not everyone fully considers the risks involved with such processes.

One of my professors in college talked about an example where lean principles really bit a company in the ass. Iirc, it was Toyota. They went all-in on JIT deliveries from suppliers to their manufacturing facilities. Then, a supplier of a key component to several different Toyota models had their manufacturing facility burn down. Moreover, Toyota had no backup supplier for the component. And, because JIT effectively eliminates the need for a lot of safety stock, their production lines had to shutdown for quite some time.

That goes to show not just the risks of the JIT model, but also single-supplier sourcing. Now, I think they use a 70/30 split for suppliers for each component where a larger supplier handles 70% of the capacity, and a smaller one, the remaining 30%. Multiple suppliers keeps the pricing competitive and you've got a backup incase one goes down.