Because managing large sites with only static HTML pages is dangerous for your health. [Object-oriented programming History]
Because through the dynamic pages, users can interact (Forum, chat) .:: www.arc.agric.za ::. .:: www4.unfccc.int ::.
Because through the dynamic pages we can offer value added services (restricted areas, various services based on user classification...)
Because the information is more easily catalogued.
Because with a few PHP pages we recall a lot of information.
Because keeping the contents up-to-date does not demand particular technical expertise and can be managed by anyone (by Davis Batistes).
It is the simplest way to to pull over a complete portal, thanks to its open source engine, it allows anyone to implement new modules or to modify and to personalize existing modules. (by Micione, .:: netbr35m.bcz.com ::. www.vizzani.net)
It is very intuitive and easy to learn (by Anonymous) .:: quomon.es ::.
It is easy to modify by those who intend to personalize the program (By Arus) .:: chromewebstore.google.com ::. [Business intelligence Study]
It is easy to use by the lesser experts among us.