It means that the "reality shows, and, on the other end of the spectrum, cable prestige television" have become so popular that "sitcoms" have become obscured from view (out of the sight and consideration by viewers).
If one thing is eclipsed by a second thing that is bigger, newer, or more important than it, the first thing is no longer noticed because the second thing gets all the attention.
The gramophone had been eclipsed by new technology such as the compact disc.
Of course, nothing is going to eclipse winning the Olympic title.
This is the same idea as a solar eclipse, for example, where the moon obscures the sun so that it can't be seen (even though it is still there).