Change watch sounds

I would like to have the ability to change the sounds from my apple watch for different notifications. We pay for custom ring tones and alert sounds, but our watches make them obsolete. Plus the same sound is used for Email and Text alerts, they have a different priority and should have a different sound. I am aware that we can adjust the haptics, but that doesn't work for me in a active environment, I can't feel the haptics. Why can't we change the sound of the alerts on an apple watch?