First your tree needs an apple, then it needs a pear, and then a fig, and after a year or two of grafting other things on you end up wishing you'd just created a cornucopia with a bunch of columns instead of joining a endless fruit because two thirds of the time you need a mix of the fruit anyway.

I'm definitely guilty of over-normalizing at least some of the time, but I'm less convinced that it's related to ORMs so much as it is to frequently having to build things without knowing how related they'll end up being in the future.