I understand the types of considerations that may make console developers not bother, but also it is a bit ridiculous on its face when they are selling physical media. But for patch-heavy games like CoD, maybe it’s a lost battle anyways, archival be damned.

But I will push back a little and say that a zsync-like differential update scheme would still be totally feasible. BD read speeds are going to be in the 100s of megabits per second, and the compute for the hash is free (ie. It’s I/O bound). You can parallelize and start downloading blocks before you’re done hashing every block on the disc. It seems likely to me that you’d still end up better off with this scheme if you have slower than gigabit download speeds (which is true for the vast majority of the US). Zsync is fairly coarse and flexible, and essentially looks like BitTorrent between two peers over HTTP if you squint. If you assume the download speed and network reliability is the bottleneck that outweighs things like disc I/O and compute, it essentially degrades gracefully to just downloading the entire update in the case that there are zero matching blocks.

Edit: I should mention that another key aspect of the setup is that there are a small number of printed disc revisions, and a small number of target download (most people will get the same game files for a given region). This means that a CDN cache will quickly find the hot blocks to serve, even without any precomputation of the diff between source and target.