If we were still in the iPod era of manual syncing, then you'd probably be right, but we're now in the "cloud consuming" era. Hence the trajectory of music piracy. When people were used to managing their CDs and MP3s, ordinary consumers absolutely did engage in opportunistic (often friend-to-friend) piracy, but then streaming came and made both legal and illegal MP3s almost a footnote
[1] Of course you can upload your own "personal documents" to your Kindle library via send-to-Kindle, but few people know that outside of tech/enthusiast circles. Even knowing what an EPUB or AZW3 is almost puts you in that bubble
Errata: rephrased the first sentence from "several hundred megabytes" to "a high-quality movie", to better explain the point that download size is rarely a barrier for piracy