WordPress values backwards compatibility and user experience. For years WordPress users have enjoyed a constant stream of new features in the core product as well as plugins. This all adds up a technical design and implementation that is not architectonically as sound as it could be.
But does this matter? WordPress has continued provide functionality and constant stream of releases where many other PHP CMSes like Drupal 8, Typo3 and eZ Publish have started major restructuring efforts with various level of success – mostly still left to be seen.
The WordPress REST API is equivalent to the one REST API in Drupal 8, for example. Does it really matter multilingual content and application data is stored “wrong” in a relational database (MySQL) that was originally built for blog posts and a a few info pages? What advantage does a blogger really get from switching to a platform powered with Node.js and MongoDB?
There is little immediate business or editor value in major change undertaking done in Drupal 8, other than being “better”. Front end technologies such as Relay, Flux and React look like a better investment for Automattic than a complete rewrite of an old backend platform to do the same old thing.
The fact seems to be that WordPress is good enough for the majority of content management needs. Barring any catastrophic security issues and as long as they can keep the user experience ahead of other options I can’t see this changing – WordPress is good enough as is.
In the meanwhile the WordPress-based eCommerce platform WooCommerce is kicking ass and taking names in in the online commerce market. Decoupling WooCommerce from WordPress is very hard, so any kind of rewrite of WordPress seems like a monumental undertaking.
Time will show whether the technical debt WordPress has accumulated is similar to that of the United States – it needs not be paid.