It’s a function of ZFS itself. Data that is to be written to the drives is first written to RAM, then transferred to the drives. One of the benefits of this is that if you are moving a file that is smaller than the available RAM, your transfer won’t appear to be limited to the write speed of the drives.
It wasn’t so much “not mind” as it was “put up with” since there was no real alternative for the average person. Also, there’s the remarkable ability of the human brain to filter out inputs it deems unnecessary. Bad smells that are a constant presence end up being filtered out.