I can weigh in here. I hate WordPress because:
- There are no application logs, so it's very difficult to debug
- The architecture is nearly entirely event-driven, so collisions between plugins and themes are common and nearly impossible to detect (because there are no logs)
- The code is very messy and primitive. It relies heavily on global variables. It becomes even more difficult to debug and more prone to hacking
- Unlike nearly every other app/CMS I've seen, it does not let you specify a path and URL in a configuration file, so migrating it between servers is problematic and usually time-intensive
- The themes are really full-blown PHP layers, so they can have all the problems of bad code everywhere including crashing the application and crashing
- Customizations become increasingly difficult the more you try to deviate from what WP has built in.
- It is an inefficient app -- it takes thousands of operations and about twice the time to complete the same task MODX could complete in a fraction of the time using a fraction of the operations.
But probably the thing that annoys me most about WordPress is that it's soooo popular and so many people think that the way that it does things is "normal" or even "the correct way". It is not. I've had to fix so many disasters created by WordPress "developers" who created "solutions" that were every bit as problematic as the WP core. In short, WP has educated a whole group of developers with bad examples and shown them instead what
not to do. WP has trained users that "
there's a plugin that fixes every problem" when the reality of development is far more complicated -- WP users tend to completely be ignorant about the underlying problems, and that becomes a really difficult discussion when you have to talk with your client about how and why the thing they fell in love with (WP's simplicity) is only one part of the app that is causing many other problems preventing their site from scaling.
Lots more detailed info in my book, but that's the nutshell.
https://leanpub.com/modx-vs-wordpress