Your comment is basically agreeing with the parent comment. The free WYSIWYG version of WP was more accessible for laypersons to build their own site and add plugins as they went along. Developers noticed that and started building for WP over other platforms, betting that those layperson-made sites would eventually need features beyond a contact form (appointment scheduling, ecommerce storefronts, sandboxed customer account creation, etc.)
Ecosystem was a huge driver. But even before that, so so easy to get going. 5 minute guided install, if you're doing it yourself. Many web hosting providers auto-installed for you. No one could touch that ease to just get going.
I once did a review of CMSs to see "is there anything better out there?" Literally scores of options. At one point seemed like everyone had tried their hand at building a CMS. Installed maybe a dozen of the most promising. It was all very meh. Some had this nice feature or that (e.g. WYSIWYG editing, back when that wasn't table stacks). But overall, none seemed substantially better that WP, Drupal and Joomla among them. Most of them seemed blighted by comparison. Drupal and Joomla included. Nothing else out there seemed worthy of investing time and energy into.
While true, I think it's more correct to say that the determining factor is which television news media people most readily consume.
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