"One standout statistic was that projects with clear requirements documented before development started were 97 percent more likely to succeed"

The issue with a majority of projects are the requirements aren't always clear from the start or even if they are it tends to deviate while the project is in progress. Agile tries to mitigate that by allowing teams to be able to react more easily to changing requirements.

That being said not many companies understand or implement agile correctly, unfortunately.