In my experience, it's much more of a momentum killer and context switch to research an annotation than a function call.

First of all, in most IDEs, it's very quick to jump to a function's actual definition to investigate such questions as "What if both of the arguments are < 0?" or "Is null an acceptable argument?". With annotations, you'll often go-to-definition and be staring at an almost empty class that hopefully has a docstring. This is because the annotations, themselves, don't actually do anything- you have to go find the code that actually checks for the annotation and does stuff.

In my experience, the docs are often not good enough when I run into a problem. I was wrestling with some strange behavior with JacksonXML some time ago, and I had a very hard time figuring out what went wrong because Jackson has so many options and they don't actually all compose well, so it's not even about figuring out what one option/annotation does- it's about figuring out what happens when I set OptX=1 and OptY=4 at the same time. Unfortunately, the docs only tell me what is supposed to happen when OptX=1 and what's supposed to happen with OptY=4, but nobody has decided to document every single combination of every single setting in the library.