A friend of mine, skeptical of the series of court cases where musical writers claim ownership of similar songs, wondered "how many pleasing combinations of chords or notes can be created before everything that follows might be considered evocative or a remix of its predecessors".
But a musical composition is so much more than just a sequence of notes on paper. There are so many dimensions along which compositions can be placed: multiple instruments, voices, pacing, things which brilliant artists understand on a subconscious level but which we are a long way from even being able to formalize. It's akin to the breadth of expression possible with letters. Any order of letters seems obvious in retrospect, and billions of words are written every day, yet no one has accidentally recreated the plot of Don Quixote. I mean heck, two generations ago there are entire genres of music that had never even been imagined. There are surely hundreds more musical genres that haven't been imagined yet.
Lots of people have directly and indirectly taken inspiration from Don Quixote, much like, say, Yankee Hotel Foxtrot takes inspiration from "Revolution no. 9". But the space of possible stories isn't so crowded that anyone has written a story that accidentally also features a novel-besotted wannabe warrior leading a series of misadventures where he concocts patently false scenarios with the help of a more clear-eyed assistant in his thrall. Some people, of course, purposely write an updated DQ! That's my point: the world of stories is wide open, not crowded; accidental similarities are tenuous. When the similarity is higher, as with DQ's influence on The Idiot, City of Glass or The Moor's Last Sigh, it turns out to have been intentional.
When someone has a musical innovation like, say, Teddy Riley's New Jack Swing, and it sweeps through the musical landscape, you see how much new musical composition draws from the field of existing ideas (and as opposed to coinciding with existing ideas through a sort of pigeonhole principle). You can practically see an idea like using voices as percussion in R&B sweeps its way through the memeosphere, from Bone Thugs 'n Harmony to Destiny's Child.
And much like with plagiarism in the written word, there's actually less gray area in practice than you might expect. So many turns of phrase and rhythms and patterns are borrowed from the landscape of subconscious reference, and brief deliberate copying. But then you have times that someone says the same eight words in a row that were in someone else's speech and it's 100% clear that the line was lifted altogether.
Similarly, in music there are tons and tons of times a sequence of 5 or 10 notes is going to match some existing song closely. I imagine algorithms are finding these for some clever troll as we speak! But the similarity in Lana del Rey's case goes way beyond the 40-odd notes (modulo an arpeggio or two) that match Radiohead's. The relative length of those notes, the relationship to the chords in the accompanying instrumentation, the story they tell--you'd need millions of parallel universes with no Creep before you'd get a song this similar.
It can seem strange that building specifically on others' ideas is so accepted in, say, the startup world and the world of novels, but so punished in music. Uber doesn't own anyone else's "Uber for X" (unless they get a BS patent). But think how much easier it would be to make, say, a good punk album where you just do a reworded version of a Bon Iver song here, a Cat Power song there, than to really write those songs from scratch.
The world of possible music composition isn't crowded. The world of possible stories isn't crowded. Most great music and most great stories haven't been written yet!
Don't be fooled by the relative stagnation of pop music in the last 15 years. Infinite music hasn't been written yet. More spookily, infinite music will never be written. It's not crowded in there--it's lonely!