The prevalence (and success) of lawsuits in regard to songs that that do not sample, but "sound" similar.
I am using the term loosely- but for an artist to create new music, it is nearly impossible to create something that is truly new. Now, whether that's because the artist inadvertently used a hook that is "too close" to something in the past, the artist heard it at some point and didn't realize they were using it, or the artist is paying homage (or even copying) is difficult to determine.
But the in terrorem effect of those lawsuits is incredibly high; for example, while were might be able to discuss the actual procedural issues behind the 9th COA's decision upholding the jury verdict, the loud message to most is that if there is any chance of going to the jury, you better settle.
Basically, when it comes to music (and rights holders) you are getting something similar to the patent troll effect, except copyrights last longer.
IMO, etc.