There is nothing wrong with Wordpress and the LAMP stack. It’s fine for many great use cases. It powers, and will continue to power many of the biggest sites in the world.
Static sites are a tradeoff, and you’re often dealing with other messes especially with non-technical users.
The problem isn't LAMP, the problem is wordpress. It stores state that should be in files in the database, and state that should be in the database in files, so they are tightly coupled, and you have to snapshot both at the same time.
It's also a security nightmare and runs dynamic code on every page load by default, so a fresh wordpress install in its default state will fall over when on HN on Reddit or Slashdot, unless you install third party caching plugins to avoid that.
The vast majority of those people contract out the (complicated) maintenance in keeping it secure and performant, or they get hacked and their site goes down, or they get ~no traffic so performance doesn't matter and neither does their choice of blog software.
Entire large businesses (WPEngine, for example) have been built upon the overhead costs from blog operators having to compensate for it being a bad app.
My close friend is one of the sysadmins for the WP instance mentioned in TFA. Pull back the curtain and it's pretty ugly and resource-intensive to run WP at scale; I've done it myself.
The only problem not addressed is that the browser directly interfaces with code that has access to the database and host computer. A static site generator is leagues more secure since you can lock anything that touches the database/CMS content behind multiple layers of authentication and 2fa, significantly reducing the attack surface.
Static sites are a tradeoff, and you’re often dealing with other messes especially with non-technical users.