Funny that you mention "accessible"... Because most of these components are anything but.
Modern HTML and CSS are awesome tools on their own, and are able to do so much without needing to rely on massive JavaScript bundles, but you still end up with component libraries that are <div><div><div><div> all the way down.
I think for an average landing page / small shop it's perfectly fine. They can go online faster with tools like this.
For more complex projects you'd tweak the components of course but it helps a lot that you can see the whole blocks rendered in advance and can prototype way faster this way.
Honestly the bloat and ergonomics of heavily customizable generic component libraries aren't great. Copy and pasting a simple component to make the specific customizations you want helps reduce JS ecosystem churn and dependency pain. Popularity of libraries like shadcn/ui [1] are good acknowledgements of that.
Webdev has always been a focus point for the industry's love of commoditization, unfortunately.
What these libraries don't do is confer any design sense. You still have to know how to put the components together well, which means you'll spend way more time than expected adjusting sizing, spacing, and thinking about responsive design.