It's because about a certain size, system projects are captured by the large consultancy shops, who eat the majority of the price in profit and management overhead...
... and then send the coding work to a lowest-cost someone who has never heard of quoting, etc.
And it's a vicious cycle, because the developers in those shops that do learn and mature quickly leave for better pay and management.
(Yes, there's usually a shit hot tiger team somewhere in these orgs, but they spend all their time bailing out dumpster fires or landing T10 customers. The average customer isn't getting them.)
