I think the idea is that the tags and the aria roles make it more legible to users using assistive technologies. For a significant number of aria roles, e.g. article, the recommended way to get that role is to use the corresponding HTML element. <section> is just a generic element but <header> has a banner role. Now admittedly there are a lot of HTML elements and a lot of aria roles, and I am not sure screen readers actually have different behavior for every role, but just by making a reasonable stab at it, you are doing better than many major corporations. (some of which have been sued over accessibility concerns)