There are a lot of other complex sites and business running Wordpress. Why is it a big deal when there's a new one???
Wordpress makes it very easy for users to manage website content for the end users. But for developers, simplicity depends upon personal preference.
I like the the whole project to follow a same set coding standards irrespective of whether it's a procedural paradigm or OOP or any other. But, if you look into the wordpress core, you will several sets of standards which makes it harder to follow through whenever you try to understand the core. For simpler plugins, one might not need to dive into the core but I have had a fare share of projects and plugin development where I had to go through the core. And, it still takes me some time to understand whenever I have to do so. Maybe, I might be using Wordpress for wrong reasons and wrong project (because that particular task can be easily achieved using other technologies or even if I start coding from scratch without wordpress), but clients are always right and I have to use the technologies they prefer.
I'm a full stack web developer looking for interesting freelance opportunities. I've been working with ASP.NET for over 2 years now and PHP (Drupal and Wordpress) for more than 3 years. I have helped quite a few clients through odesk to get their job done. I am a quick learner and am excited to work on other stacks.