Your sentence can be understood in two ways, I'll answer the question "Why use domElement.attrname instead of the corresponding domElement.setAttribute('attrname') and domElement.getAttribute('attrname')?".
It can look cleaner (matter of taste). It looks like a native JS assignment, and it's shorter.
For open and hidden, it's way more intuitive and convenient to set and get booleans than testing the existence of the corresponding HTML attribute (Still not a fan of this thing, years after having learned this).
(but maybe you meant "Why use domElement.randomprop instead of something like domElement.dataset.randomprop"?)
It can look cleaner (matter of taste). It looks like a native JS assignment, and it's shorter.
For open and hidden, it's way more intuitive and convenient to set and get booleans than testing the existence of the corresponding HTML attribute (Still not a fan of this thing, years after having learned this).
(but maybe you meant "Why use domElement.randomprop instead of something like domElement.dataset.randomprop"?)