Because it's trying to teach you how SAS actually works not to just pass an exam. I'd prefer to hire a person who understood the PDV than one who didn't, regardless of whether or not they pass the exam. Personally, I don't find the certifications super useful except maybe for your first job and at that point I expect to train you anyways.
Beyond that, you'll get tested on your skills in the interview by any decent company, this could include simple questions such as when is a variable initialized in the PDV or how does RETAIN work, to a full out take-home exam that asks you to analyze a data set.
All that being said, I did the certification exam myself a decade ago and agree on the datalines statement issue mentioned by @shelby62b, but beyond that the guide definitely helped me pass the exam.
Good Luck on your exam.
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