• It compresses much better, by a lot, as zlib/deflate is an ancient algorithm made back when computers only had a few megabytes of ram.

      Nowadays though, zstd seems to be replacing both of them, as at max level it compresses about as well as xz while also being faster. Nevertheless, many programs link against all the common compression algorithms (xz/zlib/zstd/bz2) to support everything