Jamstack is not the same thing as WordPress
WordPress and Jamstack are not the same things, architecturally or pragmatically. This can cause confusion if you're used to building websites the old way.
Wordpress is a platform for building websites. Jamstack is an architecture for building websites.
Jamstack combines multiple services and platforms to create faster, more secure, and overall better websites and web apps.
As WordPress is a blogging platform, it's fairly quick to set it up for a basic website. However, as more features and functions get added, costs quickly ramp up due to Wordpress's poor ability to scale
The initial costs for setting up Jamstack are higher than with WordPress because Jamstack is an architecture and requires some work to set up the Frontend, CMS, and configuration. Regardless, Jamstack is more cost-efficient in the long run as new features take less time to implement after the initial setup.
WordPress uses slow server-side rendering. Combined with an outdated set of technologies and programming languages like PHP makes WordPress very slow.
Jamstack delivers static files that are pre-built and optimized before users even load them.
In WordPress, content management is built into the platform; combining the content and presentation layer. This is problematic, to begin with: it becomes harder to manage and use the same content in multiple media channels.
Wordpress started out as a blogging platform and it's a very poor choice for any serious content management for obvious reasons.
With WordPress, our Frontend pages do not actually exist as files when users want to view them. This means that on each page load the files must be built on the go on a server somewhere. We call this dynamic rendering.
With Jamstack, we're using Static Site Generators to build static files that are already built and ready before users want to view them. This increases website performance, security, and reduces hosting costs significantly.
Static files already exist when we fetch them. We can serve millions of users concurrently without ever having to worry about crashing web servers.
WordPress needs a webserver to run. Everything done on WordPress must be done "in the Backend" and the output is what you see on your browser.
Jamstack does not have a backend. Everything we do with Jamstack is done directly in the browser through a set of APIs which eliminates the need for a web server. You can't crash a server if you don't have one.
Conclusion: WordPress is an outdated way to build websites
WordPress started out as a simple blogging platform and over the years it has evolved to something it was never supposed to be, causing a plethora of problems for performance, scalability, security, and software development.
Wordpress does not have a structured way of building websites that we could in Computer Science terms define as an architecture.
Jamstack is an architecture specifically designed to fix the problems we experience with WordPress.