Because part of their job, if they are good at it, is to present some data, measure how customers are responding to it, and then tweaking said data to get a better response. If you make it too hard for them to “tweak” it, then they will be more reluctant to tweak it. Thereby doing a poorer job.

Them being able to easily change the website is critical for them to be able to do their job. As in most things in life, it is a balance that needs to be achieved and not one thing that trumps everything else.

As others have said, WP gives them a way to easily change the data that they are responsible for. It should be the devs/systems engineers responsibility to make that data present as a static web page using plugins or caching layers and that should be transparent to the marketers.

The marketers care quite a lot about the readers. After all, their goal is to reach them with glorious content so they do something.

This leads them to aim for “reasonably performant for the users” as part of optimizing the package of reader + marketer experience.

In that view, IT requirements such as security rank between “should be standard” to “don’t really care” (at least until the first compromise).

How would you go about collecting the user requirements of the readers? Do they pay for the development?

The mass of readers don't have the same requirements as HackerNews commenters. Proof is that content on wordpress still gets viewed and apparently, leads to sales.

Better editor performance, more agility, the faster they can test stuff, the faster they can check what works -> better marketing.

Imagine if you were told that you had to do all of your software development work in notepad, because for whatever reason that lead to better optimized code… would you be ok with that?

It's marketing, alright? Users are cattle to be milked, their requirements matter only to the degree it keeps them on the farm, which means not much.