Because the content is mostly YouTube videos and others hosted by media sites. I don't think it's a infraction to post embeded videos from those sites.
It's copyright infringement, still, because they are now hosting the music in a place that the copyright holders have no control over. That's a perfect reason to shut 'em down.
And if WhoSampled.com has ads, they are now making money off of material they have no right to.
If I remember correctly; Rap Genius almost got shutdown for the same thing. But, now, it seems they only post Spotify links, to songs, as opposed to YouTube links, like they used to.
Complex also stopped doin' that for those "Best Of..." lists they do.
EDIT: double post