What do you mean by dynamic website ?
Dynamic websites are based on time tested CMS (content management systems) where designing and content are treated separately.
In layman language the website designing in dynamic website is independent of content.So you can modify and change the content very easily without any rework of designing.
Also dynamic websites have mobile friendly responsive layout and highly scale able in long run.
A dynamic website has a lot of features and functions that are very costly in static website.