Some players (myself not included) value the standard elf visual theme remaining distinct to blood elves, or simply the faction divide in general. So this request will naturally be met with resistance. It is also a very long standing debate with much heat on both sides.
Also, there is already a thread for discussing customization options for void elves and blood elves:
https://us.forums.blizzard.com/en/wow/t/continuation-of-new-customisation-options-for-void-elves-blood-elves-misc-high-elves/593526