By design HTML pages represent a way to view and browse information. Originally, an HTML page included the text to be shown in its own body, plus some links to external, and mostly remote, documents or sites. In recent times, however, an HTML page has seen its role changing and becoming more and more akin to a container of other objects. This change is somewhat related to the introduction of the "Active Content", and the increased spreading of the Web. This has had a double effect: the content of an HTML page has become richer and the information to be shown has been distributed among different pages.
To put it another way, HTML has evolved to become a surface capable of containing literally any kind of data. Today, if you download a page (or if you save a page while browsing on the Internet) you will almost certainly only get the template of the page or a sort of layout for it. Each of today's Web pages is filled with several images, applets, various objects, and references to other local or remote pages.
This is especially true of Intranet-based applications, and more generally for those applications that adopt a Web-based interface, or that are somehow tightly bound to the Internet.
Scriptlets are HTML pages that take their place in just this context. Scriptlets are commonly rich in images, might contain ActiveX controls, and—more likely—other Scriptlets or links to other HTML pages. Since Scriptlets are reusable and distributable too, that's why packaging isn't a secondary issue.