I don’t see why Vulcans need to change any more than the rest of them do.
I’m not a fan of “human” aliens to begin with. Why make them aliens if they’re nearly identical to humans? May as well make them human offshoots.
Humanoid.*
https://tvtropes.org/pmwiki/pmwiki.php/Main/HumanAliens
The reason why the different races are humanoid is because they are all offshoots from the same parent species, but not from humans. Humans are also offshoots.
http://memory-alpha.wikia.com/wiki/The_Chase_(episode)
http://memory-alpha.wikia.com/wiki/Ancient_humanoid
Yeah, I’m aware of that junk science explanation.