Your question is totally misdirected and should be directed at core developers on wordpress.org.
You are also totally missing the whole point of the core bundled themes. The main purpose of bundled themes are to showcase new developments in core and what the core developers find interesting. They are not there to please the masses with pedantic link colours or outrageous graphics and backgrounds.
Furthermore, the bundled themes are like any base themes available, they give developers a very basic platform/starting point to work from. It is your responsibility as developer to modify these base themes as needed to suite your particular needs.
Just stop and think for one moment, take the popular Underscores base theme (to which I have no affiliation to BTW). Just like the bundled themes, it is meant to be used as a skeleton framework onto which you can build a theme on. Just think now, if the developers of Underscores go and suddenly incorporate colorful links and some other elaborate crap into the base, it would drive theme developers up the wall as they would now first need to take care of removing all these useless extras before they can start development on something that makes sense to them.
TO CONCLUDE
The bundled themes, like the new twentysixteen theme, are not meant to aesthetically please the masses and to conform to someone else guidelines of what they think a theme should be or not be. The bundled themes are purely there to showcase core developments and improvements, and also serves as a base theme (like any other base theme available) which developers can use as a starting base on which they can create their own awesome theme on