Why should one choose WordPress as a CMS (Content Management System)?
I think the main reason is the ease with which you can make changes.
Are you aiming for good SEO? A general SEO plugin, a caching plugin (like LiteSpeed Cache or WP Rocket), and a WebP plugin (Imagify, Smush) might do wonders. Lazy loading (a3 Lazy Load) images could also help.
Interested in a specific thing, a micro-mini-small-tiny thing you specifically want, but which, generally, is rather hard to get done internally, by a programmer? There’s likely a plugin for that.
Do you want to change how the website looks? Choose a paid template, do some customizations, and you’re good to go.
The thing is, each and every thing you want to get done with WordPress can get done in other platforms. You can code HTML from scratch, you can choose another platform, you can make your own CMS.
But it just gets harder and harder, as you administer more things.
If you have a one-page website, you can consider having it done in plain HTML, although even for this WordPress might help with a template and solutions for better performance (speed).
But if you manage things like content, users, security, speed for a larger website, WordPress is just the easier path. Lots of providers „fight” to get a good SEO to their users. Lots of providers of plugins compete to get good plugins. Lots of theme creators try to solve the needs of the aesthetics of users.
It’s just easier with WordPress.