A major factor supporting evolution over big up-front design is the drift in system requirements over time. Even on large military like projects, apparently there's "discovery"--and the more years that pass, the more requirements change.
But if anything, all development is the search for the search for the requirements. Some just value writing them down.
They do change, especially if projects take years.
Not only do people tend not to read, or read well, there is a lot on inherent ambiguity in english--so even if not written stupidly there may be surprises.
"Requirements" changed on just about every project I was on. I remember once asking the business owner if he could simplify some requirements cuz they were really complicated to develop well, and he replied Certainly--he was trying to put out something he thought would be easy for us to build.