The existing site is a pretty unappealing design and is extremely overcrowded; this has been complained about for years.
The existing design seems to do a good job of using the space available to convey a large amount of important and relevant information, with very little effort required from the viewer.
For example, a viewer of the existing site can quickly get to various types of documentation right away, without having to click on a link to visit a dedicated "Documentation" page, like with the new design. The same goes for news and community details, as well. An inefficient, unnecessary extra link click or press is now needed to get to very core information.
It isn't worth making an informational website look "pretty" if that means ruining its ability to effectively convey information.
Also, the old homepage immediately gives a sense that Haskell is mature - with separate links about the language, books, libraries, IDEs, etc. The new webpage does not convey anything at all.