Everything in the Symfony/Doctrine ecosystem that uses annotations does so as an option for those who prefer them. If you don't like them, you can usually just as easily use YAML or XML or PHP configuration.

Most developers seem to like them (brevity, locational grouping of concerns), so they tend to get treated as a default, but they're not the only option or the only one treated as a first-class choice. Like much of new-PHP, this also seems to be something largely borrowed from the Java world, it's hardly something new or invented by PHP.