[gmarx]

Those are just the very low interest rates the central bank sets. In practice there will always be higher rates for higher risk loans, especially corporate bonds. The point is valid to some extent but must take account of all investment alternatives and the risk.

That said, I can't help but intuit that these valuations are the result of too much cheap money. The closest phenomenon is probably rich people bidding up fine (and otherwise) art. Seriously, do economists study the difference between extra cash in the hands of very rich people vs everyone else?