Jonas Grumby wrote:
Later Treks have developed a Trek history that says Vulcans were very involved in Earth's first "baby steps" into space and were ubiquitous (and overbearing) on Earth through much of that time.
Even though this was conceived later, it still correlates well with TOS.
Because even though Vulcan was part of the Federation, most Vulcans were Vulcan ambassadors or something similar and not many chose to join Starfleet. I believe Spock had at least some influence on why there were so many more Vulcan Starfleet officers a century later. And naturally, a lot more was known about Vulcans by the 24th century.