Plenty of people dislike Drupal, or WordPress, or Magento
I can't speak for Drupal or Magento, but WordPress's codebase is a world of pain. I've written a few plugins in the past, and the WordPress code is simply hell to work with.
Drupal is ok, but a bit old-fashioned and quirky. It's highly callback/hook based, which is fine, but it doesn't always have hooks where you need them, in which case it gets pretty ugly.
Magento is on a whole other level of suck. I worked on a highly customized Magento site 3 years ago, and it was the worst experience of my professional career - lousy software and client-from-hades.
The Magento folder structure is just completely insane...some of the templates are like 8 or 9 subfolders deep, and it's the huge mashed up pile of Zend Framework and homegrown MVC, none of which is well documented (Since after all, they want to push you to paid support...)
Oh, and to further cement the suck, the main database tables are in EAV form. Tons of fun to be had.
I can't speak for Drupal or Magento, but WordPress's codebase is a world of pain. I've written a few plugins in the past, and the WordPress code is simply hell to work with.