The GMAT conducted by GMAC has been conducted over the last 68 years since its launch in 1954 and GMAC itself says that doing well in the examination requires more than 200 hours of dedicated preparation.
The test designers have designed the test in such a manner that it is not possible for someone to just show up to the test center and sit for the exam. It is considered the most difficult B School entrance exam mainly because the questions change based on how you answered the previous questions in the section. This recursive and evolving nature of the examination. This is what catches most students off guard because everyone goes in expecting a number of hard questions which would be static. The dynamic nature of the examination makes it difficult for many people. Another issue that most people face is in the Quantitative Section if they do not have a mathematics-based background. Verbal Reasoning is difficult for people who don’t have English as a first language. All these reasons make GMAT a difficult nut to crack and getting a score upwards of 700 requires dedication and perseverance.