The Wii came with a composite cable for maximum compatibility and component video for high quality. In 2006, many people still had CRTs with no HDMI and there's not a whole lot of visible difference between component and hdmi.

In 2016, HDMI is a much better choice. Leaving it out would be strange, and saving the cost of outputting analog is worth it.

At this point it's cheaper to have just HDMI output rather than some sort of composite/component. Plus, the Wii couldn't achieve anything above 480p/576i... this has upscaling to 1080p for the "highest quality pixels" as well as its CRT shader mode.