And for more than one reason.
Sometimes it’s because the math is hard. As the science of statistics has advanced, and computers have made it practical to use ever-more-sophisticated methods, the math has gotten more sophisticated, which often means just plain harder. It’s getting more and more difficult to stay current with the latest developments. But it’s worth the effort; as the methods have gotten more complicated, they’ve also gotten better.
But sometimes it’s for an age-old reason, which few lay people and not enough scientists (even not enough statisticians) fully appreciate, that you have to understand what your data are doing, and why. Often, you really need to feel it in your gut.