I was under the impression that the UI was pretty incidental in most judges' interpretations that platforms used mainly to locate copyrighted material were on shakier ground than platforms which incidentally, and despite ostensibly significant efforts on the part of developers to limit it, could be used to locate copyright material. It's not like Google doesn't get hit by content-provider lawsuits either, it's just that they're big enough to usually get a settlement agreed on favourable terms and far too big to be bankrupted by legal costs, which is a wider and more general problem with litigation.
Ironically I'm writing this listening to YouTube streaming in the background: a far superior free way to locate and listen to music without paying for it than most of the early pirate platforms ever could have hoped to be.