The 5-paragraph essay is often the last essay format one learns seriously. We spend the most time teaching it and no other essay format even comes close. A one semester writing course freshmen year in college does not count.
Also, just because some people can run well with 10 pound weights strapped to each leg doesn't mean it's a good idea to run with weights strapped to your legs. I've seen great 5-paragraph essays, but then again, I've also seen some great Visual Basic programs as well. These things serve as great starting points, but it is important to progress beyond them as you become more educated.
I think of 5 paragraph essays as a construction used by teachers so they can evaluate how well a student is learning the process, akin to "showing your work" in mathematics. More of a scaffold for the learning process than anything else.
Also, just because some people can run well with 10 pound weights strapped to each leg doesn't mean it's a good idea to run with weights strapped to your legs. I've seen great 5-paragraph essays, but then again, I've also seen some great Visual Basic programs as well. These things serve as great starting points, but it is important to progress beyond them as you become more educated.