There's lots of sampling. (Been happening since the late 80's, sampling the the 60's and 70's) (Here's One: Bone Thugs n Harmony - It's All Mo Thug vs Isaac Hayes - You Make Me Live)
Also, non-direct sampling, or using part of the melody but changing it up a lot, but still sounding similar (Gravy - Smoove vs Red Hot Chili Peppers - Stone Cold Bush)
I like sampling in hip-hop, but I think for pop and other artists it doesn't really ring well. (cough cough Mariah Carey)
(Though the company probably owned the rights) But I couldn't tell you how many times every popular Soul/Funk Artist has been sampled and put into a beat.
You have to figure most melodies are memorable theme songs that have nothing to do with the actual thing. So like, the notes in Star Wars do not directly sound like a space war movie, but its own theme, then that theme is related to Star Wars. So next time you hear the theme song, you know, oh yeah, Star Wars! If you see Marvel movies, they don't have memorable themes. They use background music or noises that fit the environment. Which is safe, fits the scene, but does not get stuck in someone's head like a famous melody.
Most melody writers in the MAINSTREAM are dead. There's lots of voice sampling and filtering. (Logic, LOL)
The new trap rap is just repetitive auto tune and mumbling, not to mention the lyrics aren't even telling a story.
Seriously, the attention spans are so small these days, its like most kids these days like 4-measure beats instead of an entire song. Lots of sampling and filtering so much these days to produce a feeling, its not even about the notes anymore. The underground musicians like me and others will rise some day! The industry has no soul so they rely on royalties from the dead and new industry puppets.
I've been making up some melodies on my piano. They come from the soul. If I didn't hear them in my head first, I wouldn't of been able to create them on keyboard.