[CGMthrowaway]

Good point, OP describes "firms" e.g. large established organizations, and ignores early stage startups for the most part. I think that fact and your comment illuminate another reason for the high salaries - namely:

A huge raison detre to create and sustain a "firm" in the first place is stability. That stability extends on all fronts - stable base of customers, stable base of revenue, stable base of shareholder returns, and stable base of compensation for employees. Therefore, it is expected that there would be some looseness/slip/"irrationally high" or however you want to think about it, in the salaries. An early-stage startup by comparison is dealing with a different problem and purpose.

[bee_rider]

This might be kind of tangential, but—if people are working pretty hard at early stage start-ups with the intent of having their start-up bought (presumably by a large company), then the large companies must be doing something, right? Clearly the startup employees think it is worthwhile to create a good product (the company to be bought). Which means they think there will be some reward based on the quality of the start-up they create. Which means they think the large company has some way of distinguishing between high and low quality start-ups.

That’s a thing the corporation does, I guess.

[tsunamifury]

And stable labor availability for high load periods, even if rare.