The various studies have found ONE area where piracy actually affects sales: The first few weeks that a movie is in the theaters. If it's widely available digitally, that notably cuts into box-office sales.
...Later, it doesn't matter.
Music piracy is strongly tied to bigger purchases.
Ebook piracy is so tiny there are no studies about its economic effects. There's ranting about how many unauthorized downloads there are, and publishers who refuse to renew contracts based on finding pirate ebooks available - but nothing about how ebook piracy actually cuts into ebook profits in the industry as a whole.
There's claims that the industry loses over $300 million/year due to piracy. This claim is shared everywhere - based on a 2017 report by digimarc, which includes no source data - and it assumes that every unauthorized download is a missing full-price sale instead of "if I can't read that one, I'll read something else." (And that's aside from the bundle downloads where someone was only interested in one title and will never look at the others again.)
The piracy will continue at least until publishers sort out how to allow used ebooks. Which they could do - DRM could let you transfer ownership of an ebook from your device to someone else's - but they don't want to; many publishers opt out of Kindle's "two week lending, no more than twice" program, much less letting people actually give their books away.
...Nobody became an avid reader by reading full-price books of which they were the original owner. They borrowed books. They were given books other people had already read. They found abandoned books and read those.
Imagine someone saying "Oh I have these books on my shelf in case I want to re-read them, but I would never let anyone else read them." Imagine if someone bought a book or two a week, and then threw them in the shredder when they were done reading them.
Book culture is a sharing culture. And publishers have been trying to stop that for over a century, and they want ebooks to be their perfect "one purchase = one reader" system.
If they want to reduce ebook piracy, they need to figure out how to let teens give each other the book they're finished reading. How to let teachers buy a few copies a year to give out to students who seem interested. How to put a stack of ebooks on the office "Share Books" digital shelf for anyone to pick up.
Because right now, the story is "you can't even leave your ebooks to your heirs in your will." And it doesn't matter what kind of sophistry they use to justify this claim... the end result is going to be, "well, then people are going to share books without their permission." Just like they've always done.