Amazon, Microsoft, Google, they all have a broad range of products and services. Google is probably the least diverse, relying too much on search, which makes their business riskier, and it's (probably) why their p/e multiple has always been the lowest of the tech megacaps. Nvidia's multiple is on the low side right now, so perhaps the market agrees that their risk is too concentrated.

> they can easily pay to make the debt collectors go away.

Sure, if it didn't come at the same time as all their other customers pulling back, and lots of other debt collectors simultaneously knocking on the door, and a spike in the cost of capital (read: stock starts crashing).