Why has WordPress been so resilient?

Plugins and themes. WP integrates with everything and has enough over the shelf for 70% of companies to run their blogs/sites. The enterprise offering also allows for complete customization, which is why we see so many large organizations still on the platform (they are also somewhat resistant to changes, but that's another topic

The alternatives, like Sanity, Contentful, and Webflow are either too simplistic or too robust to answer to the needs to most companies.

It’s easy to install, easy to update, easy to write extensions for it and it has always put out decent, standards-based markup.

Why use anything else?

It became popular when there weren't many CMSs that non-tech people could easily install and use. It now has first-mover advantage and an entire ecosystem of plugins. In addition to this, there are entire companies dedicated to making sites based on Wordpress.

To overcome this is a daunting task because you need to convince non-tech people to move to a new solution and have something that already has a 15-year head start.

In a word: ecosystem.

Finding a WP dev is easy.

Likely finding a plugin to do some special-ish functionality as easy.

These two things fuel the fire.

Back in the day it was, "No one gets fired for buying IBM." Today that sentiment applied to WordPress.

Because many want a website that is accessible and more of a whiteboard than a piece of art.

WordPress, if maintained properly, gives a chance at that.

Plugins, themes and not beholden to the whims of a SaaS company.