This is also what I was thinking. But let's continue that train of thought... Now your site is a hybrid of static and dynamic content with two separate systems (probably a static site builder plus this serverless comment system). Why not go all the way to a CMS?
Having separate systems is (at least in my understanding and experience) a core design feature of the Jamstack.
Your question is valid. Why not go all the way to a CMS? If the author wants dynamic features AND doesn't want to build them himself, he might want to reconsider Wordpress.
Because that's not considered cool anymore and doesn't give you the opportunity to play with lots of different tools for no reason other than over-engineering.
The other comment mentions a technically valid point about separation of concerns and delegating maintenance to separate teams (essentially the same value proposition as microservices), but in the real world, is this an actual problem for 90% of websites out there, especially when talking about simple, personal or small-business websites? I don't think so.
Text content in a database is unversioned and only accessible through SQL queries in sophisticated dedicated clients; while content in markdown files can be changed with plain text editors and treated just like source code, getting all the advantages of branching, diffing and merging versions among multiple users.
Think about whether you'd like to work with all your source code stored inside a CMS like Wordpress instead of VCS like Git, and you'll begin to understand why Static Website Generators are a good thing for the people responsible of updating the content.
And several third-party developers are building user-friendly CMSs on top of it.
I also use Wordpress for serveral small/mid sized personal and F&F blogs.
I don't think comparing the comment options in Wordpress to the comment options in Jamstack applications is fair. Wordpress is a complete CRM designed for blogs/modular websites. The Jamstack is a design pattern; it's not supposed to include the kitchen sink.
Like @qeternity mentioned, the A in Jamstack stands for APIs. The author only mentioned the ability to hosts comments in Wordpress (or another CRM). Why not roll your own comment system? Sure, that's extra work, but it's also very doable if you're building a Jamstack application (again, it's not a one-click solution -- Wordpress already exists for that).
> As a result, my own blog, which is a Jamstack site, doesn’t support comments! What do I do if I want feedback on a blog post? I add a link to a corresponding tweet, asking to add a comment there. I myself feel ashamed at this compromise, but given my site’s stack, I don’t see how I can solve it. I still like my blog as a Jamstack, though, because it’s fast, it’s free, and I create all the blog posts in Markdown using VSCode. But I can’t create a community!
I don't have a "free" solution for you. But you could use a storage option like Dynamo DB, create an AWS Lambda endpoing (with API gateway) to add/get comments, and return them as JSON to your Jamstack application. Boom. A comments system. Pricewise, it shouldn't go over the AWS free tier for Lambda. I could literally spin this up in an afternoon -- let's do it this weekend if you're in.