Often enough the deadlines are set in stone within the contract and every milestone is defined ahead of time as well. I've worked with many such companies over the years and its always the exact same story. Some of them are even considered tech giants today.
It's also telling that I consider every single one of these project to be of mediocre quality at best from an engineering point of view. Thing is, our customers usually bleed so much money they barely notice it could be done any better.
People in charge of these projects usually don't know anything about software engineering and add more importance in pleasing investors in the short-term than producing value in the long-term.