There are a number of challenges that, together, are specific to the WordPress platform:

- WordPress's documentation for plugin development is not great, especially for new plugin developers. Somebody recently posted a link on HN to a small WP plugin they had developed, and it took only a few minutes to spot several things that were a bit wrong with their plugin. It wasn't their fault; the only way to know these things are wrong is by having some trial-and-error experience with the platform. There are a variety of plugin templates floating around, many of them aren't kept up to date, and none of them are designed to guide new plugin developers through all of the process.

- WP core largely allows plugin developers to do whatever they want. There are no built-in guardrails or restrictions on how to do things like handle user input or file uploads. You can choose to use WP's APIs, or ignore them and roll your own. Because of the first issue, developers often roll their own.

- The WP ecosystem is highly commercialized. WP site owners are conditioned to pay for features, and developers are incentivized to build plugins as cheaply as possible and charge for them.

- Stock out-of-the-box WP is basically just a blogging engine. Any other feature you might want to add gets delivered as a separate plugin. Because of the commercialization aspect, it's more common to install 5 different plugins to handle 5 features, rather than one "suite" plugin.

- It's really easy to install a plugin. There's a store. You enter a search term and click "install". Non-technical site owners do this all the time. In an ideal world, that would be really cool, but the downside is that they have no ability to evaluate the quality or safety of different plugins.

- So, most WP sites end up looking like an accreting disk of plugins. I've seen sites with nearly a hundred plugins installed.

- WP has some pretty good auto-update features baked in -- critical updates can be automatically installed and regular automatic updates can be enabled -- but a busted update can still break a site, and because of the commercialization of plugins, license and renewal problems can prevent security updates from getting installed. Because of the a la carte aspect of the WP ecosystem, dependencies can creep in that cause complications with updates. Every agency I've worked with that has WP sites has got some stale or broken updates on one or more of their sites. I've yet to see an agency that has everything fully up to date; it takes dedicated effort to do that, and once the development phase of a site is over and done with, site owners and agencies/developers don't want to continue sinking a ton of money into maintenance. They want fire-and-forget.

- WP has entirely ignored all of the modern changes to PHP development. There's no built-in support for composer. WP is PHP 8-compatible, but doesn't take advantage of its features. Because every WP database contains a hairy mix of configuration, content, and sometimes code, you can't do proper branch development for entire WP sites. There was a project that tried to drag WP kicking and screaming into modern branch development (https://versionpress.com/), but the release of Gutenberg forced these developers to start over and they walked away. This is exactly the sort of problem WP core should be addressing, but they aren't interested.

- This all means that the most talented developers largely want nothing to do with WordPress. Well-managed development processes are extremely painful, there's money in it but the money's better elsewhere, maintenance is a drag, and you too often have to troubleshoot some other plugin developer's conflict with your code.

- Last but not least, there's a "code review" process involved in uploading a WP plugin to their plugin repository, but it's not great. They have some really misguided notions of "security". I worked on a project that integrated a modern code editor into a plugin, which would have been a step in the right direction for managing one aspect of a WP site. (You often need a way to deploy small bits of custom code on a per-page or per-category basis, and managing these little bits of code with existing tooling is terrible.) This update got rejected by WP's security team. We had a lot of back-and-forth about it; their position was that having a modern code editor embedded in the site makes it less secure. They couldn't explain how it was different from any other of the built-in customizations available to site administrators, they just didn't like the idea of it. A plain text box for snippets? Sure! Copy-and-paste random stuff you find on the web? Sure! Using WP core's built-in editor for the functions.php file? Sure! Embedding CodeMirror? No way!

Altogether, it's a really big mess and I don't foresee it ever getting better. WP core can't make any of the big changes that would be needed to address some of these because it would cause too much friction with users, agencies, and the rotten plugin ecosystem.

I've had an arms-length relationship with WP for years, essentially seeing it as a valuable tool for non-savvy people to quickly and cheaply DIY a website, but WP is actively hostile towards modern development practices and after my last exchange with their review team I gave up on the platform for good. Dealing with WordPress hurts my soul every time. I'd rather do anything else.