> The sales guys are at the top. They are generally competent. Proof = they sold a massive deal.
I do understand what you meant here, and it's mostly right. But there are also obvious exceptions.
You can often make a sale by promising more than your competitors. If your competitors' bids are calibrated by what's actually possible, and yours isn't, then you'll win the bid... and then, years later, be unable to deliver what was specified, and have to renegotiate. But hey, you won the bid!
I guess that, if the market doesn't keep track of these renegotiations and failures-to-deliver, this is the optimum strategy over the short- and even medium-term. But it gets your company known to devs as a company that chews up and spits out talent. Devs that get stuck on projects trying to do the (literally) impossible, slogging forward each day with the knowledge that all of this is going to be ripped out when the deadlines pass and the renegotiation hits, don't tend to recommend to their friends the companies where they had to do that. So, over the long-term, this is a recipe for a talent shortage.
But, like you said, there's always contractors: fresh pools of devs who never signed up to work for something like IBM, headed by either unscrupulous or just plain naive management willing to take on such jobs with literally-impossible specs.