Optimization can be a moving target!
Many of these changes only help on newer processors, rather than being speedups that would have worked since zlib was written. Some are about using instruction-level parallelism that just wasn't available years back, and a few changes relate to other specific changes in CPUs, like using bigger tables to better exploit bigger caches or using specific new instructions.
You could say something related about gains from more modern compression formats: their design decisions make sense in today's hardware context, where DEFLATE's made sense in the 90s. For example, a 4MB history window is reasonable today but wouldn't have been when RAM was much more expensive and therefore limited. Folks were making smart decisions both then and now!