Vulpy and Ninetales are most afraid of getting hunted down for their cuteness. You see, hunters prefer to attack Pokemon for their coating rather than strength. Ninetales has beautiful fur that would be worth money, because the humans want their fur to wear.
1. Because it looks beautiful.
2. Because it's much warmer than normal fur.
3. Ninetales comes from a sort of tiger, and tigers have beautiful coats, so why not just hunt a Ninetales.
Vulpix, on the other hand wouldn't have to worry about this until it evolves. Ninetales would have to worry about this at the time it is in now. Thankfully, if the Pokemon-government heard about this and started to enforce laws to protect the Ninetales family. All is now well in Ninetales' world.